diff --git a/src/libraries/System.Memory/src/System/Buffers/Text/Base64.cs b/src/libraries/Common/src/System/Buffers/Text/Base64.cs
similarity index 100%
rename from src/libraries/System.Memory/src/System/Buffers/Text/Base64.cs
rename to src/libraries/Common/src/System/Buffers/Text/Base64.cs
diff --git a/src/libraries/System.Memory/src/System/Buffers/Text/Base64Decoder.cs b/src/libraries/Common/src/System/Buffers/Text/Base64Decoder.cs
similarity index 98%
rename from src/libraries/System.Memory/src/System/Buffers/Text/Base64Decoder.cs
rename to src/libraries/Common/src/System/Buffers/Text/Base64Decoder.cs
index b0c491a5beaba7..143fb6f76a2d00 100644
--- a/src/libraries/System.Memory/src/System/Buffers/Text/Base64Decoder.cs
+++ b/src/libraries/Common/src/System/Buffers/Text/Base64Decoder.cs
@@ -477,22 +477,6 @@ private static unsafe void Avx2Decode(ref byte* srcBytes, ref byte* destBytes, b
             destBytes = dest;
         }
 
-        // This can be replaced once https://github.com/dotnet/runtime/issues/63331 is implemented.
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static Vector128<byte> SimdShuffle(Vector128<byte> left, Vector128<byte> right, Vector128<byte> mask8F)
-        {
-            Debug.Assert((Ssse3.IsSupported || AdvSimd.Arm64.IsSupported) && BitConverter.IsLittleEndian);
-
-            if (Ssse3.IsSupported)
-            {
-                return Ssse3.Shuffle(left, right);
-            }
-            else
-            {
-                return AdvSimd.Arm64.VectorTableLookup(left, Vector128.BitwiseAnd(right, mask8F));
-            }
-        }
-
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static unsafe void Vector128Decode(ref byte* srcBytes, ref byte* destBytes, byte* srcEnd, int sourceLength, int destLength, byte* srcStart, byte* destStart)
         {
diff --git a/src/libraries/System.Memory/src/System/Buffers/Text/Base64Encoder.cs b/src/libraries/Common/src/System/Buffers/Text/Base64Encoder.cs
similarity index 97%
rename from src/libraries/System.Memory/src/System/Buffers/Text/Base64Encoder.cs
rename to src/libraries/Common/src/System/Buffers/Text/Base64Encoder.cs
index 9eb60032b65e4f..8538db086ca62f 100644
--- a/src/libraries/System.Memory/src/System/Buffers/Text/Base64Encoder.cs
+++ b/src/libraries/Common/src/System/Buffers/Text/Base64Encoder.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
@@ -17,6 +18,22 @@ namespace System.Buffers.Text
     /// </summary>
     public static partial class Base64
     {
+        // This can be replaced once https://github.com/dotnet/runtime/issues/63331 is implemented.
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static Vector128<byte> SimdShuffle(Vector128<byte> left, Vector128<byte> right, Vector128<byte> mask8F)
+        {
+            Debug.Assert((Ssse3.IsSupported || AdvSimd.Arm64.IsSupported) && BitConverter.IsLittleEndian);
+
+            if (Ssse3.IsSupported)
+            {
+                return Ssse3.Shuffle(left, right);
+            }
+            else
+            {
+                return AdvSimd.Arm64.VectorTableLookup(left, Vector128.BitwiseAnd(right, mask8F));
+            }
+        }
+
         /// <summary>
         /// Encode the span of binary data into UTF-8 encoded text represented as base64.
         /// </summary>
diff --git a/src/libraries/System.Memory/src/System.Memory.csproj b/src/libraries/System.Memory/src/System.Memory.csproj
index 7294197f7a962f..1f2e8675a5e2f5 100644
--- a/src/libraries/System.Memory/src/System.Memory.csproj
+++ b/src/libraries/System.Memory/src/System.Memory.csproj
@@ -25,9 +25,9 @@
     <Compile Include="System\Buffers\SequenceReader.cs" />
     <Compile Include="System\Buffers\SequenceReader.Search.cs" />
     <Compile Include="System\Buffers\SequenceReaderExtensions.Binary.cs" />
-    <Compile Include="System\Buffers\Text\Base64.cs" />
-    <Compile Include="System\Buffers\Text\Base64Decoder.cs" />
-    <Compile Include="System\Buffers\Text\Base64Encoder.cs" />
+    <Compile Include="$(CommonPath)System\Buffers\Text\Base64.cs" />
+    <Compile Include="$(CommonPath)System\Buffers\Text\Base64Decoder.cs" />
+    <Compile Include="$(CommonPath)System\Buffers\Text\Base64Encoder.cs" />
     <Compile Include="System\Runtime\InteropServices\SequenceMarshal.cs" />
     <Compile Include="System\Text\EncodingExtensions.cs" />
   </ItemGroup>
diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index d978ef0b8c4883..27588a75dc15ce 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -243,6 +243,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Configuration\Assemblies\AssemblyVersionCompatibility.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Context.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Convert.Base64.cs" />
+    <Compile Include="$(CommonPath)System\Buffers\Text\Base64.cs" />
+    <Compile Include="$(CommonPath)System\Buffers\Text\Base64Encoder.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Convert.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\CoreLib.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\CurrentSystemTimeZone.cs" />
diff --git a/src/libraries/System.Private.CoreLib/src/System/Convert.cs b/src/libraries/System.Private.CoreLib/src/System/Convert.cs
index 5b212556c684e7..398cb5ddf74b23 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Convert.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Convert.cs
@@ -6,6 +6,8 @@
 using System.Globalization;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Buffers.Text;
+using System.Text;
 
 namespace System
 {
@@ -2336,7 +2338,16 @@ public static string ToBase64String(ReadOnlySpan<byte> bytes, Base64FormattingOp
             }
 
             bool insertLineBreaks = (options == Base64FormattingOptions.InsertLineBreaks);
-            string result = string.FastAllocateString(ToBase64_CalculateAndValidateOutputLength(bytes.Length, insertLineBreaks));
+            int outputLength = ToBase64_CalculateAndValidateOutputLength(bytes.Length, insertLineBreaks);
+
+            if (!insertLineBreaks && bytes.Length >= 64)
+            {
+                Span<byte> utf8Result = outputLength <= 256 ? stackalloc byte[256] : new byte[outputLength];
+                Base64.EncodeToUtf8(bytes, utf8Result, out int _, out int _);
+                return Encoding.Latin1.GetString(utf8Result);
+            }
+
+            string result = string.FastAllocateString(outputLength);
 
             unsafe
             {