diff --git a/github/provider.go b/github/provider.go
index 8f44c9509..6da23a539 100644
--- a/github/provider.go
+++ b/github/provider.go
@@ -158,6 +158,7 @@ func Provider() *schema.Provider {
 			"github_issue_labels":                                                   resourceGithubIssueLabels(),
 			"github_membership":                                                     resourceGithubMembership(),
 			"github_organization_block":                                             resourceOrganizationBlock(),
+			"github_organization_custom_property":                                   resourceGithubOrganizationCustomProperty(),
 			"github_organization_custom_role":                                       resourceGithubOrganizationCustomRole(),
 			"github_organization_project":                                           resourceGithubOrganizationProject(),
 			"github_organization_security_manager":                                  resourceGithubOrganizationSecurityManager(),
diff --git a/github/resource_github_organization_custom_property.go b/github/resource_github_organization_custom_property.go
new file mode 100644
index 000000000..882d2cde0
--- /dev/null
+++ b/github/resource_github_organization_custom_property.go
@@ -0,0 +1,358 @@
+package github
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"github.com/google/go-github/v66/github"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/validation"
+)
+
+const (
+	ORG_ACTORS          = "org_actors"
+	ORG_AND_REPO_ACTORS = "org_and_repo_actors"
+)
+
+// This file implements a custom schema and (un)marshalling logic for GitHub organization custom properties.
+// The upstream GitHub SDK (github.CustomProperty) supports only a single string value for the `default_value` field,
+// which is not compatible with the MULTI_SELECT property type that requires a list of default values.
+// To work around this limitation, we define a customPropertyExtended struct that embeds github.CustomProperty
+// and overrides the `default_value` field with a flexible interface that can handle string, []string, or null values.
+// Custom JSON marshalling and unmarshalling methods are implemented to ensure compatibility with the GitHub API
+// while preserving type correctness and Terraform expectations.
+type customPropertyExtended struct {
+	github.CustomProperty
+
+	// Overrides the original DefaultValue to support string, null, and []string.
+	DefaultValueOverride interface{} `json:"default_value,omitempty"`
+}
+
+func (c *customPropertyExtended) MarshalJSON() ([]byte, error) {
+	// Marshal base struct to map
+	base, err := json.Marshal(c.CustomProperty)
+	if err != nil {
+		return nil, err
+	}
+
+	var baseMap map[string]interface{}
+	if err := json.Unmarshal(base, &baseMap); err != nil {
+		return nil, err
+	}
+
+	// Override default_value
+	if c.DefaultValueOverride != nil {
+		baseMap["default_value"] = c.DefaultValueOverride
+	}
+
+	return json.Marshal(baseMap)
+}
+
+func (c *customPropertyExtended) UnmarshalJSON(data []byte) error {
+	// Unmarshal the JSON into a map to isolate default_value
+	var m map[string]json.RawMessage
+	if err := json.Unmarshal(data, &m); err != nil {
+		return err
+	}
+
+	// Extract and remove default_value before unmarshalling the embedded struct
+	var rawDefault json.RawMessage
+	if v, ok := m["default_value"]; ok {
+		rawDefault = v
+		delete(m, "default_value")
+	}
+
+	// Re-marshal the map without default_value
+	sanitized, err := json.Marshal(m)
+	if err != nil {
+		return err
+	}
+
+	// Unmarshal the sanitized JSON into the embedded CustomProperty struct
+	if err := json.Unmarshal(sanitized, &c.CustomProperty); err != nil {
+		return err
+	}
+
+	// Manually unmarshal default_value based on its type
+	if len(rawDefault) > 0 {
+		// Try to unmarshal as a string
+		var s string
+		if err := json.Unmarshal(rawDefault, &s); err == nil {
+			c.DefaultValueOverride = s
+			return nil
+		}
+
+		// Try to unmarshal as a []string
+		var list []string
+		if err := json.Unmarshal(rawDefault, &list); err == nil {
+			c.DefaultValueOverride = list
+			return nil
+		}
+
+		// Handle null value
+		if string(rawDefault) == "null" {
+			c.DefaultValueOverride = nil
+			return nil
+		}
+
+		return fmt.Errorf("invalid format for default_value: %s", string(rawDefault))
+	}
+
+	return nil
+}
+
+func (c *customPropertyExtended) GetDefaultValueOverride() ([]string, error) {
+	switch value := c.DefaultValueOverride.(type) {
+	case string:
+		return []string{value}, nil
+	case []string:
+		return value, nil
+	case nil:
+		return nil, nil
+	default:
+		return nil, fmt.Errorf("custom property value couldn't be parsed as a string or a list of strings: %s", value)
+	}
+}
+
+func resourceGithubOrganizationCustomProperty() *schema.Resource {
+	return &schema.Resource{
+		Create: resourceGithubOrganizationCustomPropertyCreateOrUpdate,
+		Update: resourceGithubOrganizationCustomPropertyCreateOrUpdate,
+		Read:   resourceGithubOrganizationCustomPropertyRead,
+		Delete: resourceGithubOrganizationCustomPropertyDelete,
+		Importer: &schema.ResourceImporter{
+			StateContext: func(ctx context.Context, d *schema.ResourceData, meta interface{}) ([]*schema.ResourceData, error) {
+				if err := resourceGithubOrganizationCustomPropertyRead(d, meta); err != nil {
+					return nil, err
+				}
+				return []*schema.ResourceData{d}, nil
+			},
+		},
+		CustomizeDiff: func(ctx context.Context, diff *schema.ResourceDiff, meta interface{}) error {
+			// Validate the relationship between required and default_value.
+			// If the property is marked as required, a non-empty default value must be provided.
+			// If the property is not required, then a default value must not be set.
+			required := diff.Get("required").(bool)
+			defaultValue := expandStringList(diff.Get("default_value").(*schema.Set).List())
+			if required {
+				if len(defaultValue) == 0 {
+					return errors.New("default_value can not be empty")
+				}
+			} else {
+				if len(defaultValue) != 0 {
+					return errors.New("default_value is only allowed if required is true")
+				}
+			}
+
+			// Validate that for MULTI_SELECT and SINGLE_SELECT types,
+			// all default values must be included in the list of allowed values.
+			propertyType := diff.Get("type").(string)
+			allowedValues := expandStringList(diff.Get("allowed_values").(*schema.Set).List())
+			if propertyType == MULTI_SELECT || propertyType == SINGLE_SELECT {
+				if !isSubset(defaultValue, allowedValues) {
+					return errors.New("default_value must be a subset of allowed_values")
+				}
+			}
+
+			// Validate that for STRING or TRUE_FALSE properties, no allowed values are permitted.
+			// STRING type should not define allowed_values, as it's meant to be free-form text.
+			if propertyType == STRING || propertyType == TRUE_FALSE {
+				if len(allowedValues) != 0 {
+					return errors.New("allowed_values must be empty when type is STRING or TRUE_FALSE")
+				}
+			}
+
+			// Validate that for SINGLE_SELECT and STRING properties, at most one default value is permitted.
+			// An empty list or a single option is allowed, but more than one value is not supported in this context.
+			if propertyType == SINGLE_SELECT || propertyType == STRING {
+				if len(defaultValue) > 1 {
+					return errors.New("default_value must contain zero or one item when type is SINGLE_SELECT or STRING")
+				}
+			}
+
+			// Validate that for TRUE_FALSE properties, at most one default value is permitted,
+			// and if provided, it must be either "true" or "false".
+			if propertyType == TRUE_FALSE && len(defaultValue) == 1 {
+				if defaultValue[0] != "true" && defaultValue[0] != "false" {
+					return errors.New("default_value must be either \"true\" or \"false\" when type is TRUE_FALSE")
+				}
+			}
+
+			return nil
+		},
+		Schema: map[string]*schema.Schema{
+			"name": {
+				Description: "Name of the custom property.",
+				ForceNew:    true,
+				Required:    true,
+				Type:        schema.TypeString,
+			},
+			"type": {
+				Description:      "Type of the custom property",
+				ForceNew:         true,
+				Required:         true,
+				Type:             schema.TypeString,
+				ValidateDiagFunc: toDiagFunc(validation.StringInSlice([]string{SINGLE_SELECT, MULTI_SELECT, STRING, TRUE_FALSE}, false), "type"),
+			},
+			"required": {
+				Default:     false,
+				Description: "Whether the property is required.",
+				Optional:    true,
+				Type:        schema.TypeBool,
+			},
+			"default_value": {
+				Description: "Default value of the property if required.",
+				Elem: &schema.Schema{
+					Type: schema.TypeString,
+				},
+				MinItems: 1,
+				Optional: true,
+				Type:     schema.TypeSet,
+			},
+			"description": {
+				Description: "Short description of the property.",
+				Optional:    true,
+				Type:        schema.TypeString,
+			},
+			"allowed_values": {
+				Description: "An ordered list of the allowed values of the property. The property can have up to 200 allowed values.",
+				Elem: &schema.Schema{
+					Type: schema.TypeString,
+				},
+				MaxItems: 200,
+				Optional: true,
+				Type:     schema.TypeSet,
+			},
+			"values_editable_by": {
+				Default:          ORG_ACTORS,
+				Description:      "Who can edit the values of the property.",
+				Optional:         true,
+				Type:             schema.TypeString,
+				ValidateDiagFunc: toDiagFunc(validation.StringInSlice([]string{ORG_ACTORS, ORG_AND_REPO_ACTORS}, false), "values_editable_by"),
+			},
+		},
+	}
+}
+
+func resourceGithubOrganizationCustomPropertyCreateOrUpdate(d *schema.ResourceData, meta interface{}) error {
+	client := meta.(*Owner).v3client
+	orgName := meta.(*Owner).name
+	ctx := context.Background()
+
+	err := checkOrganization(meta)
+	if err != nil {
+		return err
+	}
+
+	propertyName := d.Get("name").(string)
+	propertyType := d.Get("type").(string)
+	propertyRequired := d.Get("required").(bool)
+	propertyDefaultValue := expandStringList(d.Get("default_value").(*schema.Set).List())
+	propertyDescription := d.Get("description").(string)
+	propertyAllowedValues := expandStringList(d.Get("allowed_values").(*schema.Set).List())
+	propertyValuesEditableBy := d.Get("values_editable_by").(string)
+
+	customProperty := customPropertyExtended{
+		CustomProperty: github.CustomProperty{
+			PropertyName:     &propertyName,
+			ValueType:        propertyType,
+			Required:         &propertyRequired,
+			Description:      &propertyDescription,
+			AllowedValues:    propertyAllowedValues,
+			ValuesEditableBy: &propertyValuesEditableBy,
+		},
+	}
+
+	if len(propertyDefaultValue) > 0 {
+		// The propertyDefaultValue can either be a list of strings or a string
+		switch propertyType {
+		case SINGLE_SELECT, TRUE_FALSE, STRING:
+			customProperty.DefaultValueOverride = &propertyDefaultValue[0]
+		case MULTI_SELECT:
+			customProperty.DefaultValueOverride = propertyDefaultValue
+		default:
+			return fmt.Errorf("custom property type is not valid: %v", propertyType)
+		}
+	}
+
+	u := fmt.Sprintf("orgs/%v/properties/schema/%v", orgName, propertyName)
+	req, err := client.NewRequest("PUT", u, customProperty)
+	if err != nil {
+		return err
+	}
+
+	_, err = client.Do(ctx, req, nil)
+	if err != nil {
+		return err
+	}
+
+	d.SetId(buildTwoPartID(orgName, propertyName))
+
+	return resourceGithubOrganizationCustomPropertyRead(d, meta)
+}
+
+func resourceGithubOrganizationCustomPropertyRead(d *schema.ResourceData, meta interface{}) error {
+	client := meta.(*Owner).v3client
+	ctx := context.Background()
+
+	err := checkOrganization(meta)
+	if err != nil {
+		return err
+	}
+
+	orgName, propertyName, err := parseTwoPartID(d.Id(), "orgName", "propertyName")
+	if err != nil {
+		return err
+	}
+
+	u := fmt.Sprintf("orgs/%v/properties/schema/%v", orgName, propertyName)
+	req, err := client.NewRequest("GET", u, nil)
+	if err != nil {
+		return err
+	}
+
+	var customProperty *customPropertyExtended
+	_, err = client.Do(ctx, req, &customProperty)
+	if err != nil {
+		return err
+	}
+
+	defaultValue, err := customProperty.GetDefaultValueOverride()
+	if err != nil {
+		return err
+	}
+
+	d.SetId(buildTwoPartID(orgName, customProperty.GetPropertyName()))
+	d.Set("name", customProperty.GetPropertyName())
+	d.Set("type", customProperty.ValueType)
+	d.Set("required", customProperty.Required)
+	d.Set("default_value", defaultValue)
+	d.Set("description", customProperty.GetDescription())
+	d.Set("allowed_values", customProperty.AllowedValues)
+	d.Set("values_editable_by", customProperty.GetValuesEditableBy())
+
+	return nil
+}
+
+func resourceGithubOrganizationCustomPropertyDelete(d *schema.ResourceData, meta interface{}) error {
+	client := meta.(*Owner).v3client
+	ctx := context.Background()
+
+	err := checkOrganization(meta)
+	if err != nil {
+		return err
+	}
+
+	orgName, propertyName, err := parseTwoPartID(d.Id(), "orgName", "propertyName")
+	if err != nil {
+		return err
+	}
+
+	_, err = client.Organizations.RemoveCustomProperty(ctx, orgName, propertyName)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
diff --git a/github/resource_github_organization_custom_property_test.go b/github/resource_github_organization_custom_property_test.go
new file mode 100644
index 000000000..7a056a007
--- /dev/null
+++ b/github/resource_github_organization_custom_property_test.go
@@ -0,0 +1,142 @@
+package github
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
+)
+
+func TestAccGithubOrganizationCustomProperty_CustomizeDiff_Validations(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name        string
+		config      string
+		expectError *regexp.Regexp
+	}{
+		{
+			name: "required true but default_value missing",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name    = "required_without_default"
+  type    = "string"
+  required = true
+}
+`,
+			expectError: regexp.MustCompile("default_value can not be empty"),
+		},
+		{
+			name: "default_value set but required false",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name    = "default_without_required"
+  type    = "string"
+  required = false
+  default_value = ["foo"]
+}
+`,
+			expectError: regexp.MustCompile("default_value is only allowed if required is true"),
+		},
+		{
+			name: "default_value not in allowed_values with SINGLE_SELECT",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name = "invalid_default"
+  type = "single_select"
+  required = true
+  allowed_values = ["foo", "bar"]
+  default_value  = ["baz"]
+}
+`,
+			expectError: regexp.MustCompile("default_value must be a subset of allowed_values"),
+		},
+		{
+			name: "default_value not in allowed_values with MULTI_SELECT",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name = "invalid_default"
+  type = "multi_select"
+  required = true
+  allowed_values = ["foo", "bar"]
+  default_value  = ["foo", "baz"]
+}
+`,
+			expectError: regexp.MustCompile("default_value must be a subset of allowed_values"),
+		},
+		{
+			name: "allowed_values used with STRING",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name = "string_with_allowed"
+  type = "string"
+  allowed_values = ["not", "allowed"]
+}
+`,
+			expectError: regexp.MustCompile("allowed_values must be empty when type is STRING or TRUE_FALSE"),
+		},
+		{
+			name: "allowed_values used with TRUE_FALSE",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name = "true_false_with_allowed"
+  type = "true_false"
+  allowed_values = ["true"]
+}
+`,
+			expectError: regexp.MustCompile("allowed_values must be empty when type is STRING or TRUE_FALSE"),
+		},
+		{
+			name: "multiple default_value with SINGLE_SELECT",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name = "multi_default_single_select"
+  type = "single_select"
+  required = true
+  allowed_values = ["foo"]
+  default_value  = ["foo", "bar"]
+}
+`,
+			expectError: regexp.MustCompile("defaultValue must contain zero or one item when type is SINGLE_SELECT or STRING"),
+		},
+		{
+			name: "multiple default_value with STRING",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name = "multi_default_string"
+  type = "string"
+  required = true
+  default_value  = ["foo", "bar"]
+}
+`,
+			expectError: regexp.MustCompile("defaultValue must contain zero or one item when type is SINGLE_SELECT or STRING"),
+		},
+		{
+			name: "invalid TRUE_FALSE default",
+			config: `
+resource "github_organization_custom_property" "test" {
+  name = "invalid_true_false"
+  type = "true_false"
+  required = true
+  default_value = ["maybe"]
+}
+`,
+			expectError: regexp.MustCompile("default_value must be either \"true\" or \"false\" when type is TRUE_FALSE"),
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			resource.Test(t, resource.TestCase{
+				PreCheck:  func() { skipUnlessMode(t, organization) },
+				Providers: testAccProviders,
+				Steps: []resource.TestStep{
+					{
+						Config:      tc.config,
+						ExpectError: tc.expectError,
+					},
+				},
+			})
+		})
+	}
+}
diff --git a/github/util.go b/github/util.go
index 321a201fb..eed4e6790 100644
--- a/github/util.go
+++ b/github/util.go
@@ -281,3 +281,17 @@ func deleteResourceOn404AndSwallow304OtherwiseReturnError(err error, d *schema.R
 	}
 	return err
 }
+
+func isSubset(subset, set []string) bool {
+	setMap := make(map[string]struct{}, len(set))
+	for _, item := range set {
+		setMap[item] = struct{}{}
+	}
+
+	for _, item := range subset {
+		if _, ok := setMap[item]; !ok {
+			return false
+		}
+	}
+	return true
+}