diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
index ee9f789a40fab..b0c1376611b9e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
@@ -6,6 +6,7 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
 using System.Runtime.Intrinsics.X86;
 
 #if SYSTEM_PRIVATE_CORELIB
@@ -882,7 +883,7 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
             // is not enabled.
 
             Unsafe.SkipInit(out Vector128<short> nonAsciiUtf16DataMask);
-            if (Sse41.X64.IsSupported)
+            if (Sse41.X64.IsSupported || (AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian))
             {
                 nonAsciiUtf16DataMask = Vector128.Create(unchecked((short)0xFF80)); // mask of non-ASCII bits in a UTF-16 char
             }
@@ -940,10 +941,8 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                     uint inputCharsRemaining = (uint)(pFinalPosWhereCanReadDWordFromInputBuffer - pInputBuffer) + 2;
                     uint minElementsRemaining = (uint)Math.Min(inputCharsRemaining, outputBytesRemaining);
 
-                    if (Sse41.X64.IsSupported)
+                    if (Sse41.X64.IsSupported || (AdvSimd.Arm64.IsSupported && BitConverter.IsLittleEndian))
                     {
-                        Debug.Assert(BitConverter.IsLittleEndian, "SSE41 requires little-endian.");
-
                         // Try reading and writing 8 elements per iteration.
                         uint maxIters = minElementsRemaining / 8;
                         ulong possibleNonAsciiQWord;
@@ -952,14 +951,30 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                         for (i = 0; (uint)i < maxIters; i++)
                         {
                             utf16Data = Unsafe.ReadUnaligned<Vector128<short>>(pInputBuffer);
-                            if (!Sse41.TestZ(utf16Data, nonAsciiUtf16DataMask))
+
+                            if (AdvSimd.IsSupported)
                             {
-                                goto LoopTerminatedDueToNonAsciiDataInVectorLocal;
-                            }
+                                Vector128<short> isUtf16DataNonAscii = AdvSimd.CompareTest(utf16Data, nonAsciiUtf16DataMask);
+                                bool hasNonAsciiDataInVector = AdvSimd.Arm64.MinPairwise(isUtf16DataNonAscii, isUtf16DataNonAscii).AsUInt64().ToScalar() != 0;
 
-                            // narrow and write
+                                if (hasNonAsciiDataInVector)
+                                {
+                                    goto LoopTerminatedDueToNonAsciiDataInVectorLocal;
+                                }
 
-                            Sse2.StoreScalar((ulong*)pOutputBuffer /* unaligned */, Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt64());
+                                Vector64<byte> lower = AdvSimd.ExtractNarrowingSaturateUnsignedLower(utf16Data);
+                                AdvSimd.Store(pOutputBuffer, lower);
+                            }
+                            else
+                            {
+                                if (!Sse41.TestZ(utf16Data, nonAsciiUtf16DataMask))
+                                {
+                                    goto LoopTerminatedDueToNonAsciiDataInVectorLocal;
+                                }
+
+                                // narrow and write
+                                Sse2.StoreScalar((ulong*)pOutputBuffer /* unaligned */, Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt64());
+                            }
 
                             pInputBuffer += 8;
                             pOutputBuffer += 8;
@@ -978,7 +993,16 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                             }
 
                             utf16Data = Vector128.CreateScalarUnsafe(possibleNonAsciiQWord).AsInt16();
-                            Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+
+                            if (AdvSimd.IsSupported)
+                            {
+                                Vector64<byte> lower = AdvSimd.ExtractNarrowingSaturateUnsignedLower(utf16Data);
+                                AdvSimd.StoreSelectedScalar((uint*)pOutputBuffer, lower.AsUInt32(), 0);
+                            }
+                            else
+                            {
+                                Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+                            }
 
                             pInputBuffer += 4;
                             pOutputBuffer += 4;
@@ -990,7 +1014,15 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                     LoopTerminatedDueToNonAsciiDataInVectorLocal:
 
                         outputBytesRemaining -= 8 * i;
-                        possibleNonAsciiQWord = Sse2.X64.ConvertToUInt64(utf16Data.AsUInt64());
+
+                        if (Sse2.X64.IsSupported)
+                        {
+                            possibleNonAsciiQWord = Sse2.X64.ConvertToUInt64(utf16Data.AsUInt64());
+                        }
+                        else
+                        {
+                            possibleNonAsciiQWord = utf16Data.AsUInt64().ToScalar();
+                        }
 
                         // Temporarily set 'possibleNonAsciiQWord' to be the low 64 bits of the vector,
                         // then check whether it's all-ASCII. If so, narrow and write to the destination
@@ -1000,7 +1032,15 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
 
                         if (Utf16Utility.AllCharsInUInt64AreAscii(possibleNonAsciiQWord)) // all chars in first QWORD are ASCII
                         {
-                            Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+                            if (AdvSimd.IsSupported)
+                            {
+                                Vector64<byte> lower = AdvSimd.ExtractNarrowingSaturateUnsignedLower(utf16Data);
+                                AdvSimd.StoreSelectedScalar((uint*)pOutputBuffer, lower.AsUInt32(), 0);
+                            }
+                            else
+                            {
+                                Unsafe.WriteUnaligned<uint>(pOutputBuffer, Sse2.ConvertToUInt32(Sse2.PackUnsignedSaturate(utf16Data, utf16Data).AsUInt32()));
+                            }
                             pInputBuffer += 4;
                             pOutputBuffer += 4;
                             outputBytesRemaining -= 4;
diff --git a/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs b/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs
index c4c68e966eba2..fa4602b33f429 100644
--- a/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs
+++ b/src/libraries/System.Utf8String.Experimental/src/System/Runtime/Intrinsics/Intrinsics.Shims.cs
@@ -8,6 +8,7 @@ internal static class Vector64
         public static Vector64<ulong> Create(ulong value) => throw new PlatformNotSupportedException();
         public static Vector64<uint> CreateScalar(uint value) => throw new PlatformNotSupportedException();
         public static Vector64<byte> AsByte<T>(this Vector64<T> vector) where T : struct => throw new PlatformNotSupportedException();
+        public static Vector64<uint> AsUInt32<T>(this Vector64<T> vector) where T : struct => throw new PlatformNotSupportedException();
     }
     internal readonly struct Vector64<T>
         where T : struct