diff --git a/.changelog/12496.txt b/.changelog/12496.txt
new file mode 100644
index 00000000000..ed5ca473c14
--- /dev/null
+++ b/.changelog/12496.txt
@@ -0,0 +1,3 @@
+```release-note:improvement
+client: set NOMAD_CPU_CORES environment variable when reserving cpu cores
+```
diff --git a/client/taskenv/env.go b/client/taskenv/env.go
index 1b6d4ce788f..eaed60567a2 100644
--- a/client/taskenv/env.go
+++ b/client/taskenv/env.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/hashicorp/nomad/helper"
 	hargs "github.com/hashicorp/nomad/helper/args"
+	"github.com/hashicorp/nomad/lib/cpuset"
 	"github.com/hashicorp/nomad/nomad/structs"
 	"github.com/hashicorp/nomad/plugins/drivers"
 	"github.com/zclconf/go-cty/cty"
@@ -40,6 +41,9 @@ const (
 	// CpuLimit is the environment variable with the tasks CPU limit in MHz.
 	CpuLimit = "NOMAD_CPU_LIMIT"
 
+	// CpuCores is the environment variable for passing the task's reserved cpu cores
+	CpuCores = "NOMAD_CPU_CORES"
+
 	// AllocID is the environment variable for passing the allocation ID.
 	AllocID = "NOMAD_ALLOC_ID"
 
@@ -397,6 +401,7 @@ type Builder struct {
 	// clientTaskSecretsDir is the secrets dir from the client's perspective; eg <client_task_root>/secrets
 	clientTaskSecretsDir string
 
+	cpuCores         string
 	cpuLimit         int64
 	memLimit         int64
 	memMaxLimit      int64
@@ -493,6 +498,9 @@ func (b *Builder) buildEnv(allocDir, localDir, secretsDir string,
 	if b.cpuLimit != 0 {
 		envMap[CpuLimit] = strconv.FormatInt(b.cpuLimit, 10)
 	}
+	if b.cpuCores != "" {
+		envMap[CpuCores] = b.cpuCores
+	}
 
 	// Add the task metadata
 	if b.allocId != "" {
@@ -742,6 +750,7 @@ func (b *Builder) setAlloc(alloc *structs.Allocation) *Builder {
 		// Populate task resources
 		if tr, ok := alloc.AllocatedResources.Tasks[b.taskName]; ok {
 			b.cpuLimit = tr.Cpu.CpuShares
+			b.cpuCores = cpuset.New(tr.Cpu.ReservedCores...).String()
 			b.memLimit = tr.Memory.MemoryMB
 			b.memMaxLimit = tr.Memory.MemoryMaxMB
 
@@ -788,7 +797,7 @@ func (b *Builder) setAlloc(alloc *structs.Allocation) *Builder {
 		}
 	}
 
-	upstreams := []structs.ConsulUpstream{}
+	var upstreams []structs.ConsulUpstream
 	for _, svc := range tg.Services {
 		if svc.Connect.HasSidecar() && svc.Connect.SidecarService.HasUpstreams() {
 			upstreams = append(upstreams, svc.Connect.SidecarService.Proxy.Upstreams...)
diff --git a/client/taskenv/env_test.go b/client/taskenv/env_test.go
index 32e6238169e..5d9bf75e09e 100644
--- a/client/taskenv/env_test.go
+++ b/client/taskenv/env_test.go
@@ -159,7 +159,10 @@ func TestEnvironment_AsList(t *testing.T) {
 	a := mock.Alloc()
 	a.Job.ParentID = fmt.Sprintf("mock-parent-service-%s", uuid.Generate())
 	a.AllocatedResources.Tasks["web"] = &structs.AllocatedTaskResources{
-		Cpu: structs.AllocatedCpuResources{CpuShares: 500},
+		Cpu: structs.AllocatedCpuResources{
+			CpuShares:     500,
+			ReservedCores: []uint16{0, 5, 6, 7},
+		},
 		Memory: structs.AllocatedMemoryResources{
 			MemoryMB:    256,
 			MemoryMaxMB: 512,
@@ -215,6 +218,7 @@ func TestEnvironment_AsList(t *testing.T) {
 		"NOMAD_PORT_ssh_other=1234",
 		"NOMAD_PORT_ssh_ssh=22",
 		"NOMAD_CPU_LIMIT=500",
+		"NOMAD_CPU_CORES=0,5-7",
 		"NOMAD_DC=dc1",
 		"NOMAD_NAMESPACE=not-default",
 		"NOMAD_REGION=global",
@@ -260,6 +264,7 @@ func TestEnvironment_AllValues(t *testing.T) {
 		MBits:         50,
 		DynamicPorts:  []structs.Port{{Label: "http", Value: 80}},
 	}
+	a.AllocatedResources.Tasks["web"].Cpu.ReservedCores = []uint16{0, 5, 6, 7}
 	a.AllocatedResources.Tasks["ssh"] = &structs.AllocatedTaskResources{
 		Networks: []*structs.NetworkResource{
 			{
@@ -378,6 +383,7 @@ func TestEnvironment_AllValues(t *testing.T) {
 		"NOMAD_PORT_ssh_other":                      "1234",
 		"NOMAD_PORT_ssh_ssh":                        "22",
 		"NOMAD_CPU_LIMIT":                           "500",
+		"NOMAD_CPU_CORES":                           "0,5-7",
 		"NOMAD_DC":                                  "dc1",
 		"NOMAD_PARENT_CGROUP":                       "abc.slice",
 		"NOMAD_NAMESPACE":                           "default",
diff --git a/website/content/partials/envvars.mdx b/website/content/partials/envvars.mdx
index 019603d741a..9edca49a950 100644
--- a/website/content/partials/envvars.mdx
+++ b/website/content/partials/envvars.mdx
@@ -54,6 +54,15 @@
       </td>
       <td>CPU limit in MHz for the task</td>
     </tr>
+    <tr>
+      <td>
+        <code>NOMAD_CPU_CORES</code>
+      </td>
+      <td>
+        The specific CPU cores reserved for the task in cpuset list notation.
+        Omitted if the the task does not request cpu cores. E.g. <code>0-2,7,12-14</code>
+      </td>
+    </tr>
     <tr>
       <td>
         <code>NOMAD_ALLOC_ID</code>