diff --git a/ArmPkg/Include/Library/ArmMonitorLib.h b/ArmPkg/Include/Library/ArmMonitorLib.h
index d6e13b61d6..1192ee2888 100644
--- a/ArmPkg/Include/Library/ArmMonitorLib.h
+++ b/ArmPkg/Include/Library/ArmMonitorLib.h
@@ -23,6 +23,18 @@ typedef struct {
   UINTN    Arg5;
   UINTN    Arg6;
   UINTN    Arg7;
+ #ifdef MDE_CPU_AARCH64
+  UINTN    Arg8;
+  UINTN    Arg9;
+  UINTN    Arg10;
+  UINTN    Arg11;
+  UINTN    Arg12;
+  UINTN    Arg13;
+  UINTN    Arg14;
+  UINTN    Arg15;
+  UINTN    Arg16;
+  UINTN    Arg17;
+ #endif
 } ARM_MONITOR_ARGS;
 
 /** Monitor call.
diff --git a/ArmPkg/Library/ArmMonitorLib/AArch64/ArmMonitorLib.S b/ArmPkg/Library/ArmMonitorLib/AArch64/ArmMonitorLib.S
new file mode 100644
index 0000000000..a99adf00ad
--- /dev/null
+++ b/ArmPkg/Library/ArmMonitorLib/AArch64/ArmMonitorLib.S
@@ -0,0 +1,79 @@
+//
+//  Copyright (c) 2024, Google Llc. All rights reserved.
+//
+//  SPDX-License-Identifier: BSD-2-Clause-Patent
+//
+//
+
+#include <AsmMacroIoLibV8.h>
+
+/** Monitor call.
+
+  An HyperVisor Call (HVC) or System Monitor Call (SMC) will be issued
+  depending on the default conduit. PcdMonitorConduitHvc determines the type
+  of the call: if true, do an HVC.
+
+  @param [in,out]  Args    Arguments for the HVC/SMC.
+**/
+ASM_FUNC(ArmMonitorCall)
+  // Create a stack frame
+  stp   x29, x30, [sp, #-16]!
+  mov   x29, sp
+
+  // Preserve X0 for later use
+  mov   x30, x0
+
+  // Load the SMCCC arguments values into the appropriate registers
+  ldp   x0, x1, [x30, #0]
+  ldp   x2, x3, [x30, #16]
+  ldp   x4, x5, [x30, #32]
+  ldp   x6, x7, [x30, #48]
+  ldp   x8, x9, [x30, #64]
+  ldp   x10, x11, [x30, #80]
+  ldp   x12, x13, [x30, #96]
+  ldp   x14, x15, [x30, #112]
+  ldp   x16, x17, [x30, #128]
+
+#if !defined(_PCD_VALUE_PcdMonitorConduitHvc)
+#error
+#elif _PCD_VALUE_PcdMonitorConduitHvc == 0
+  smc   #0
+#elif _PCD_VALUE_PcdMonitorConduitHvc == 1
+  hvc   #0
+#else
+#error
+#endif
+
+  // A SMCCC SMC64/HVC64 call can return up to 18 values.
+  stp   x0, x1, [x30, #0]
+  stp   x2, x3, [x30, #16]
+  stp   x4, x5, [x30, #32]
+  stp   x6, x7, [x30, #48]
+  stp   x8, x9, [x30, #64]
+  stp   x10, x11, [x30, #80]
+  stp   x12, x13, [x30, #96]
+  stp   x14, x15, [x30, #112]
+  stp   x16, x17, [x30, #128]
+
+  // Clear return values from registers
+  mov   x0, xzr
+  mov   x1, xzr
+  mov   x2, xzr
+  mov   x3, xzr
+  mov   x4, xzr
+  mov   x5, xzr
+  mov   x6, xzr
+  mov   x7, xzr
+  mov   x8, xzr
+  mov   x9, xzr
+  mov   x10, xzr
+  mov   x11, xzr
+  mov   x12, xzr
+  mov   x13, xzr
+  mov   x14, xzr
+  mov   x15, xzr
+  mov   x16, xzr
+  mov   x17, xzr
+
+  ldp   x29, x30, [sp], #16
+  ret
diff --git a/ArmPkg/Library/ArmMonitorLib/Arm/ArmMonitorLib.S b/ArmPkg/Library/ArmMonitorLib/Arm/ArmMonitorLib.S
new file mode 100644
index 0000000000..9029059cf4
--- /dev/null
+++ b/ArmPkg/Library/ArmMonitorLib/Arm/ArmMonitorLib.S
@@ -0,0 +1,49 @@
+//
+//  Copyright (c) 2024, Google Llc. All rights reserved.
+//
+//  SPDX-License-Identifier: BSD-2-Clause-Patent
+//
+//
+
+#include <AsmMacroIoLib.h>
+
+/** Monitor call.
+
+  An HyperVisor Call (HVC) or System Monitor Call (SMC) will be issued
+  depending on the default conduit. PcdMonitorConduitHvc determines the type
+  of the call: if true, do an HVC.
+
+  @param [in,out]  Args    Arguments for the HVC/SMC.
+**/
+ASM_FUNC(ArmMonitorCall)
+  push  {r4-r7}
+
+  // Preserve R0 for later use
+  mov   ip, r0
+
+  // Load the SMCCC arguments values into the appropriate registers
+  ldm   r0, {r0-r7}
+
+#if !defined(_PCD_VALUE_PcdMonitorConduitHvc)
+#error
+#elif _PCD_VALUE_PcdMonitorConduitHvc == 0
+  .arch_extension sec
+  smc   #0
+#elif _PCD_VALUE_PcdMonitorConduitHvc == 1
+  .arch_extension virt
+  hvc   #0
+#else
+#error
+#endif
+
+  // A SMCCC SMC32/HVC32 call can return up to 8 values.
+  stm   ip, {r0-r7}
+
+  // Clear return values from registers
+  mov   r0, #0
+  mov   r1, #0
+  mov   r2, #0
+  mov   r3, #0
+
+  pop   {r4-r7}
+  bx    lr
diff --git a/ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.c b/ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.c
deleted file mode 100644
index 72f71296e5..0000000000
--- a/ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.c
+++ /dev/null
@@ -1,34 +0,0 @@
-/** @file
-  Arm Monitor Library.
-
-  Copyright (c) 2022, Arm Limited. All rights reserved.<BR>
-
-  SPDX-License-Identifier: BSD-2-Clause-Patent
-
-**/
-
-#include <Library/ArmHvcLib.h>
-#include <Library/ArmMonitorLib.h>
-#include <Library/ArmSmcLib.h>
-#include <Library/PcdLib.h>
-
-/** Monitor call.
-
-  An HyperVisor Call (HVC) or System Monitor Call (SMC) will be issued
-  depending on the default conduit. PcdMonitorConduitHvc determines the type
-  of the call: if true, do an HVC.
-
-  @param [in,out]  Args    Arguments for the HVC/SMC.
-**/
-VOID
-EFIAPI
-ArmMonitorCall (
-  IN OUT ARM_MONITOR_ARGS  *Args
-  )
-{
-  if (FixedPcdGetBool (PcdMonitorConduitHvc)) {
-    ArmCallHvc ((ARM_HVC_ARGS *)Args);
-  } else {
-    ArmCallSmc ((ARM_SMC_ARGS *)Args);
-  }
-}
diff --git a/ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.inf b/ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.inf
index f504cb80f1..06fbab28b6 100644
--- a/ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.inf
+++ b/ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.inf
@@ -14,16 +14,15 @@
   VERSION_STRING                 = 1.0
   LIBRARY_CLASS                  = ArmMonitorLib
 
-[Sources]
-  ArmMonitorLib.c
+[Sources.ARM]
+  Arm/ArmMonitorLib.S
+
+[Sources.AARCH64]
+  AArch64/ArmMonitorLib.S
 
 [Packages]
   ArmPkg/ArmPkg.dec
   MdePkg/MdePkg.dec
 
-[LibraryClasses]
-  ArmHvcLib
-  ArmSmcLib
-
 [Pcd]
   gArmTokenSpaceGuid.PcdMonitorConduitHvc