diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 2f02539435..d4379372d0 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -99,6 +99,7 @@ dependencies {
     implementation(libs.androidx.compose.runtime.tracing)
     implementation(libs.androidx.core.ktx)
     implementation(libs.androidx.core.splashscreen)
+    implementation(libs.androidx.appcompat)
     implementation(libs.androidx.lifecycle.runtimeCompose)
     implementation(libs.androidx.lifecycle.viewModel.navigation3)
     implementation(libs.androidx.profileinstaller)
diff --git a/app/src/main/kotlin/com/google/samples/apps/nowinandroid/NiaApplication.kt b/app/src/main/kotlin/com/google/samples/apps/nowinandroid/NiaApplication.kt
index 4975e5d65f..bc2a8b4daf 100644
--- a/app/src/main/kotlin/com/google/samples/apps/nowinandroid/NiaApplication.kt
+++ b/app/src/main/kotlin/com/google/samples/apps/nowinandroid/NiaApplication.kt
@@ -20,11 +20,17 @@ import android.app.Application
 import android.content.pm.ApplicationInfo
 import android.os.StrictMode
 import android.os.StrictMode.ThreadPolicy.Builder
+import androidx.datastore.core.DataStore
 import coil.ImageLoader
 import coil.ImageLoaderFactory
+import com.google.samples.apps.nowinandroid.core.datastore.UserPreferences
+import com.google.samples.apps.nowinandroid.core.network.di.ApplicationScope
 import com.google.samples.apps.nowinandroid.sync.initializers.Sync
 import com.google.samples.apps.nowinandroid.util.ProfileVerifierLogger
+import com.google.samples.apps.nowinandroid.util.initializeNightModeFromPreferences
+import com.google.samples.apps.nowinandroid.util.observeNightModePreferences
 import dagger.hilt.android.HiltAndroidApp
+import kotlinx.coroutines.CoroutineScope
 import javax.inject.Inject
 
 /**
@@ -35,12 +41,24 @@ class NiaApplication : Application(), ImageLoaderFactory {
     @Inject
     lateinit var imageLoader: dagger.Lazy<ImageLoader>
 
+    @Inject
+    lateinit var userPrefsDataStore: DataStore<UserPreferences>
+
     @Inject
     lateinit var profileVerifierLogger: ProfileVerifierLogger
 
+    @Inject
+    @ApplicationScope
+    lateinit var applicationScope: CoroutineScope
+
     override fun onCreate() {
         super.onCreate()
 
+        // Initialize dark mode from user prefs
+        initializeNightModeFromPreferences(userPrefsDataStore)
+
+        observeNightModePreferences(userPrefsDataStore, applicationScope)
+
         setStrictModePolicy()
 
         // Initialize Sync; the system responsible for keeping data in the app up to date.
diff --git a/app/src/main/kotlin/com/google/samples/apps/nowinandroid/util/UiExtensions.kt b/app/src/main/kotlin/com/google/samples/apps/nowinandroid/util/UiExtensions.kt
index 20d55ab4ce..b3220732a9 100644
--- a/app/src/main/kotlin/com/google/samples/apps/nowinandroid/util/UiExtensions.kt
+++ b/app/src/main/kotlin/com/google/samples/apps/nowinandroid/util/UiExtensions.kt
@@ -16,13 +16,28 @@
 
 package com.google.samples.apps.nowinandroid.util
 
+import android.app.UiModeManager
+import android.content.Context
 import android.content.res.Configuration
+import android.os.Build
 import androidx.activity.ComponentActivity
+import androidx.annotation.RequiresApi
+import androidx.appcompat.app.AppCompatDelegate
 import androidx.core.util.Consumer
+import androidx.datastore.core.DataStore
+import com.google.samples.apps.nowinandroid.core.datastore.DarkThemeConfigProto
+import com.google.samples.apps.nowinandroid.core.datastore.UserPreferences
+import com.google.samples.apps.nowinandroid.core.model.data.DarkThemeConfig
+import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.channels.awaitClose
 import kotlinx.coroutines.flow.callbackFlow
 import kotlinx.coroutines.flow.conflate
 import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.drop
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
 
 /**
  * Convenience wrapper for dark mode checking
@@ -47,3 +62,81 @@ fun ComponentActivity.isSystemInDarkTheme() = callbackFlow {
 }
     .distinctUntilChanged()
     .conflate()
+
+/**
+ * Converts [DarkThemeConfig] to AppCompat night mode constant.
+ */
+fun DarkThemeConfig.toNightMode(): Int = when (this) {
+    DarkThemeConfig.FOLLOW_SYSTEM -> AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM
+    DarkThemeConfig.LIGHT -> AppCompatDelegate.MODE_NIGHT_NO
+    DarkThemeConfig.DARK -> AppCompatDelegate.MODE_NIGHT_YES
+}
+
+/**
+ * Maps a [DarkThemeConfig] value to the corresponding night mode setting
+ * used by UiModeManager on Android 12 (API level 31) and above.
+ */
+@RequiresApi(Build.VERSION_CODES.S)
+fun DarkThemeConfig.toUiNightMode(): Int = when(this) {
+    DarkThemeConfig.FOLLOW_SYSTEM -> UiModeManager.MODE_NIGHT_AUTO
+    DarkThemeConfig.LIGHT -> UiModeManager.MODE_NIGHT_NO
+    DarkThemeConfig.DARK -> UiModeManager.MODE_NIGHT_YES
+}
+
+/**
+ * Applies this [DarkThemeConfig] as default night mode.
+ */
+fun DarkThemeConfig.applyAsDefaultNightMode(context: Context) {
+    if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+        val uiModeManager = context.getSystemService(Context.UI_MODE_SERVICE) as UiModeManager
+        uiModeManager.setApplicationNightMode(toUiNightMode())
+    } else {
+        AppCompatDelegate.setDefaultNightMode(toNightMode())
+    }
+}
+
+/**
+ * Converts stored proto data into a DarkThemeConfig object.
+ */
+fun DarkThemeConfigProto.toDarkThemeConfig(): DarkThemeConfig = when (this) {
+    DarkThemeConfigProto.DARK_THEME_CONFIG_LIGHT -> DarkThemeConfig.LIGHT
+    DarkThemeConfigProto.DARK_THEME_CONFIG_DARK -> DarkThemeConfig.DARK
+    else -> DarkThemeConfig.FOLLOW_SYSTEM
+}
+
+/**
+ * Sets night mode from user prefs. Call in Application.onCreate() to show correct splash theme.
+ */
+fun Context.initializeNightModeFromPreferences(userPrefsDataStore: DataStore<UserPreferences>) {
+    runBlocking {
+        runCatching {
+            val darkThemeConfig = userPrefsDataStore.data
+                .first()
+                .darkThemeConfig
+                .toDarkThemeConfig()
+
+            darkThemeConfig.applyAsDefaultNightMode(this@initializeNightModeFromPreferences)
+        }.onFailure {
+            DarkThemeConfig.FOLLOW_SYSTEM.applyAsDefaultNightMode(this@initializeNightModeFromPreferences)
+        }
+    }
+}
+
+/**
+ * Observe theme changes and updates UiModeManager to prevent a bug where the first cold start
+ * uses the previous theme, while later starts use the correct one.
+ */
+fun Context.observeNightModePreferences(
+    userPrefsDataStore: DataStore<UserPreferences>,
+    scope: CoroutineScope,
+) {
+    scope.launch {
+        userPrefsDataStore.data
+            .map { it.darkThemeConfig.toDarkThemeConfig() }
+            .distinctUntilChanged()
+            .drop(1) // Skip first emission (already handled by initializeNightModeFromPreferences)
+            .collect { darkThemeConfig ->
+                darkThemeConfig.applyAsDefaultNightMode(this@observeNightModePreferences)
+            }
+    }
+}
\ No newline at end of file