diff --git a/llvm/include/llvm/ADT/Triple.h b/llvm/include/llvm/ADT/Triple.h
--- a/llvm/include/llvm/ADT/Triple.h
+++ b/llvm/include/llvm/ADT/Triple.h
@@ -233,12 +233,13 @@
     MuslX32,
 
     MSVC,
+    MSVC_Arm64EC,
     Itanium,
     Cygnus,
     CoreCLR,
     Simulator, // Simulator variants of other systems, e.g., Apple's iOS
-    MacABI, // Mac Catalyst variant of Apple's iOS deployment target.
-    
+    MacABI,    // Mac Catalyst variant of Apple's iOS deployment target.
+
     // Shader Stages
     Pixel,
     Vertex,
@@ -566,7 +567,8 @@
 
   /// Checks if the environment is MSVC.
   bool isKnownWindowsMSVCEnvironment() const {
-    return isOSWindows() && getEnvironment() == Triple::MSVC;
+    return isOSWindows() && (getEnvironment() == Triple::MSVC ||
+                             getEnvironment() == Triple::MSVC_Arm64EC);
   }
 
   /// Checks if the environment could be MSVC.
@@ -575,6 +577,11 @@
            (isOSWindows() && getEnvironment() == Triple::UnknownEnvironment);
   }
 
+  // Checks if we're using the Windows Arm64EC ABI.
+  bool isWindowsArm64EC() const {
+    return getEnvironment() == Triple::MSVC_Arm64EC;
+  }
+
   bool isWindowsCoreCLREnvironment() const {
     return isOSWindows() && getEnvironment() == Triple::CoreCLR;
   }
diff --git a/llvm/lib/Support/Triple.cpp b/llvm/lib/Support/Triple.cpp
--- a/llvm/lib/Support/Triple.cpp
+++ b/llvm/lib/Support/Triple.cpp
@@ -263,6 +263,7 @@
   case GNUILP32: return "gnu_ilp32";
   case Itanium: return "itanium";
   case MSVC: return "msvc";
+  case MSVC_Arm64EC: return "msvc_arm64ec";
   case MacABI: return "macabi";
   case Musl: return "musl";
   case MuslEABI: return "musleabi";
@@ -605,6 +606,7 @@
       .StartsWith("musleabi", Triple::MuslEABI)
       .StartsWith("muslx32", Triple::MuslX32)
       .StartsWith("musl", Triple::Musl)
+      .StartsWith("msvc_arm64ec", Triple::MSVC_Arm64EC)
       .StartsWith("msvc", Triple::MSVC)
       .StartsWith("itanium", Triple::Itanium)
       .StartsWith("cygnus", Triple::Cygnus)
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
@@ -745,7 +745,7 @@
 
   std::unique_ptr<MCObjectTargetWriter>
   createObjectTargetWriter() const override {
-    return createAArch64WinCOFFObjectWriter();
+    return createAArch64WinCOFFObjectWriter(TheTriple);
   }
 };
 }
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.h b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.h
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.h
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.h
@@ -32,6 +32,7 @@
 class MCTargetOptions;
 class MCTargetStreamer;
 class Target;
+class Triple;
 
 MCCodeEmitter *createAArch64MCCodeEmitter(const MCInstrInfo &MCII,
                                           MCContext &Ctx);
@@ -51,7 +52,8 @@
 createAArch64MachObjectWriter(uint32_t CPUType, uint32_t CPUSubtype,
                               bool IsILP32);
 
-std::unique_ptr<MCObjectTargetWriter> createAArch64WinCOFFObjectWriter();
+std::unique_ptr<MCObjectTargetWriter>
+createAArch64WinCOFFObjectWriter(const Triple &TheTriple);
 
 MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
                                                  formatted_raw_ostream &OS,
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFObjectWriter.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFObjectWriter.cpp
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFObjectWriter.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64WinCOFFObjectWriter.cpp
@@ -30,8 +30,10 @@
 
 class AArch64WinCOFFObjectWriter : public MCWinCOFFObjectTargetWriter {
 public:
-  AArch64WinCOFFObjectWriter()
-      : MCWinCOFFObjectTargetWriter(COFF::IMAGE_FILE_MACHINE_ARM64) {}
+  AArch64WinCOFFObjectWriter(const Triple &TheTriple)
+      : MCWinCOFFObjectTargetWriter(TheTriple.isWindowsArm64EC()
+                                        ? COFF::IMAGE_FILE_MACHINE_ARM64EC
+                                        : COFF::IMAGE_FILE_MACHINE_ARM64) {}
 
   ~AArch64WinCOFFObjectWriter() override = default;
 
@@ -159,6 +161,7 @@
   return true;
 }
 
-std::unique_ptr<MCObjectTargetWriter> llvm::createAArch64WinCOFFObjectWriter() {
-  return std::make_unique<AArch64WinCOFFObjectWriter>();
+std::unique_ptr<MCObjectTargetWriter>
+llvm::createAArch64WinCOFFObjectWriter(const Triple &TheTriple) {
+  return std::make_unique<AArch64WinCOFFObjectWriter>(TheTriple);
 }
diff --git a/llvm/test/MC/AArch64/arm64ec.s b/llvm/test/MC/AArch64/arm64ec.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/AArch64/arm64ec.s
@@ -0,0 +1,4 @@
+// RUN: llvm-mc -triple aarch64-pc-windows-msvc_arm64ec -filetype=obj %s -o - | llvm-objdump -d -r - | FileCheck %s
+// CHECK: file format coff-arm64ec
+// CHECK: add x0, x1, x2
+add x0, x1, x2