diff --git a/core/src/main/kotlin/com/mitteloupe/cag/core/generation/versioncatalog/VersionCatalogUpdater.kt b/core/src/main/kotlin/com/mitteloupe/cag/core/generation/versioncatalog/VersionCatalogUpdater.kt
index c2c5e5d..f22055c 100644
--- a/core/src/main/kotlin/com/mitteloupe/cag/core/generation/versioncatalog/VersionCatalogUpdater.kt
+++ b/core/src/main/kotlin/com/mitteloupe/cag/core/generation/versioncatalog/VersionCatalogUpdater.kt
@@ -91,8 +91,9 @@ class VersionCatalogUpdater(
         val resolvedPluginIdToAliasMutable = existingPluginIdToAlias.toMutableMap()
         val pluginRequirements = mutableListOf<PluginRequirement>()
         val pluginAliasToIdMutable = existingPluginAliasToId.toMutableMap()
+        val uniqueDesiredPlugins = dependencyConfiguration.plugins.distinctBy { it.id }
 
-        for (desired in dependencyConfiguration.plugins) {
+        for (desired in uniqueDesiredPlugins) {
             val existingAlias = existingPluginIdToAlias[desired.id]
             if (existingAlias != null) {
                 resolvedPluginIdToAliasMutable[desired.id] = existingAlias
@@ -131,8 +132,9 @@ class VersionCatalogUpdater(
         val resolvedLibraryModuleToAliasMutable = existingLibraryModuleToAlias.toMutableMap()
         val libraryRequirements = mutableListOf<LibraryRequirement>()
         val libraryAliasToModuleMutable = existingLibraryAliasToModule.toMutableMap()
+        val uniqueDesiredLibraries = dependencyConfiguration.libraries.distinctBy { it.module }
 
-        for (desired in dependencyConfiguration.libraries) {
+        for (desired in uniqueDesiredLibraries) {
             val existingAlias = existingLibraryModuleToAlias[desired.module]
             if (existingAlias != null) {
                 resolvedLibraryModuleToAliasMutable[desired.module] = existingAlias
@@ -201,7 +203,7 @@ class VersionCatalogUpdater(
         fileCreator.createFileIfNotExists(catalogFile) { "" }
 
         val pluginRequirements =
-            dependencyConfiguration.plugins.map { desired ->
+            dependencyConfiguration.plugins.distinctBy { it.id }.map { desired ->
                 PluginRequirement(
                     key = desired.key,
                     id = desired.id,
@@ -210,7 +212,7 @@ class VersionCatalogUpdater(
             }
 
         val libraryRequirements =
-            dependencyConfiguration.libraries.map { desired ->
+            dependencyConfiguration.libraries.distinctBy { it.module }.map { desired ->
                 LibraryRequirement(
                     key = desired.key,
                     module = desired.module,
diff --git a/core/src/test/kotlin/com/mitteloupe/cag/core/generation/VersionCatalogUpdaterTest.kt b/core/src/test/kotlin/com/mitteloupe/cag/core/generation/VersionCatalogUpdaterTest.kt
index 85b9c38..93d6d6d 100644
--- a/core/src/test/kotlin/com/mitteloupe/cag/core/generation/VersionCatalogUpdaterTest.kt
+++ b/core/src/test/kotlin/com/mitteloupe/cag/core/generation/VersionCatalogUpdaterTest.kt
@@ -4,6 +4,7 @@ import com.mitteloupe.cag.core.fake.FakeFileSystemBridge
 import com.mitteloupe.cag.core.generation.filesystem.FileCreator
 import com.mitteloupe.cag.core.generation.versioncatalog.DependencyConfiguration
 import com.mitteloupe.cag.core.generation.versioncatalog.LibraryConstants
+import com.mitteloupe.cag.core.generation.versioncatalog.LibraryConstants.TEST_MOCKITO_ANDROID
 import com.mitteloupe.cag.core.generation.versioncatalog.PluginConstants
 import com.mitteloupe.cag.core.generation.versioncatalog.SectionEntryRequirement.LibraryRequirement
 import com.mitteloupe.cag.core.generation.versioncatalog.SectionEntryRequirement.PluginRequirement
@@ -24,6 +25,145 @@ class VersionCatalogUpdaterTest {
         classUnderTest = VersionCatalogUpdater(FileCreator(FakeFileSystemBridge()))
     }
 
+    @Test
+    fun `Given libraries include library twice when createOrUpdateVersionCatalog then deduplicates`() {
+        // Given
+        val (projectRoot, catalogFile) =
+            createProjectWithCatalog(
+                initialContent =
+                    """
+                    [versions]
+                    kotlin = "2.2.10"
+                    compileSdk = "36"
+                    minSdk = "24"
+                    """.trimIndent()
+            )
+
+        val dependencyConfiguration =
+            DependencyConfiguration(
+                versions = emptyList(),
+                libraries = listOf(TEST_MOCKITO_ANDROID, TEST_MOCKITO_ANDROID),
+                plugins = emptyList()
+            )
+        val expectedCatalog =
+            """
+            [versions]
+            kotlin = "2.2.10"
+            compileSdk = "36"
+            minSdk = "24"
+            mockitoAndroid = "2.28.6"
+
+            [libraries]
+            test-mockito-android = { module = "com.linkedin.dexmaker:dexmaker-mockito-inline", version.ref = "mockitoAndroid" }
+
+            """.trimIndent()
+
+        // When
+        classUnderTest.createOrUpdateVersionCatalog(projectRootDir = projectRoot, dependencyConfiguration = dependencyConfiguration)
+        val actualCatalog = catalogFile.readText()
+
+        // Then
+        assertEquals(expectedCatalog, actualCatalog)
+    }
+
+    @Test
+    fun `Given plugins include plugin twice when createOrUpdateVersionCatalog then deduplicates`() {
+        // Given
+        val (projectRoot, catalogFile) =
+            createProjectWithCatalog(
+                initialContent =
+                    """
+                    [versions]
+                    kotlin = "2.2.10"
+                    compileSdk = "36"
+                    minSdk = "24"
+                    """.trimIndent()
+            )
+
+        val dependencyConfiguration =
+            DependencyConfiguration(
+                versions = emptyList(),
+                libraries = emptyList(),
+                plugins = listOf(PluginConstants.KOTLIN_JVM, PluginConstants.KOTLIN_JVM)
+            )
+        val expectedCatalog =
+            """
+            [versions]
+            kotlin = "2.2.10"
+            compileSdk = "36"
+            minSdk = "24"
+
+            [plugins]
+            kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
+
+            """.trimIndent()
+
+        // When
+        classUnderTest.createOrUpdateVersionCatalog(projectRootDir = projectRoot, dependencyConfiguration = dependencyConfiguration)
+        val actualCatalog = catalogFile.readText()
+
+        // Then
+        assertEquals(expectedCatalog, actualCatalog)
+    }
+
+    @Test
+    fun `Given libraries include library twice when createOrReplaceVersionCatalog then deduplicates`() {
+        // Given
+        val projectRoot = createTempDirectory(prefix = "newCatalogDedupLib").toFile()
+
+        val dependencyConfiguration =
+            DependencyConfiguration(
+                versions = emptyList(),
+                libraries = listOf(TEST_MOCKITO_ANDROID, TEST_MOCKITO_ANDROID),
+                plugins = emptyList()
+            )
+        val expectedCatalog =
+            """
+            [versions]
+            mockitoAndroid = "2.28.6"
+
+            [libraries]
+            test-mockito-android = { module = "com.linkedin.dexmaker:dexmaker-mockito-inline", version.ref = "mockitoAndroid" }
+
+            """.trimIndent()
+
+        // When
+        classUnderTest.createOrReplaceVersionCatalog(projectRootDir = projectRoot, dependencyConfiguration = dependencyConfiguration)
+        val actualCatalog = File(projectRoot, "gradle/libs.versions.toml").readText()
+
+        // Then
+        assertEquals(expectedCatalog, actualCatalog)
+    }
+
+    @Test
+    fun `Given plugins include plugin twice when createOrReplaceVersionCatalog then deduplicates`() {
+        // Given
+        val projectRoot = createTempDirectory(prefix = "newCatalogDedupPlugin").toFile()
+
+        val dependencyConfiguration =
+            DependencyConfiguration(
+                versions = emptyList(),
+                libraries = emptyList(),
+                plugins = listOf(PluginConstants.KOTLIN_JVM, PluginConstants.KOTLIN_JVM)
+            )
+        val expectedCatalog =
+            """
+            [versions]
+            kotlin = "2.2.10"
+
+            [plugins]
+            kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
+
+            """.trimIndent()
+
+        // When
+        classUnderTest.createOrReplaceVersionCatalog(projectRootDir = projectRoot, dependencyConfiguration = dependencyConfiguration)
+        val actualCatalog = File(projectRoot, "gradle/libs.versions.toml").readText()
+
+        // Then
+        assertEquals(expectedCatalog, actualCatalog)
+    }
+
     @Test
     fun `Given no catalog file when createOrUpdateVersionCatalog then does nothing`() {
         // Given