diff --git a/docs/auth.md b/docs/auth.md
index e8daec6..0b624a2 100644
--- a/docs/auth.md
+++ b/docs/auth.md
@@ -110,6 +110,8 @@ harness auth setscope --org myorg --project myproject
 
 `auth status` handles SATs differently: instead of calling `GET /ng/api/user/currentUser`, it calls `POST /ng/api/token/validate` and shows the service account identity. 403 responses on the Account/Org/Project checks are shown as warnings (not errors) since the SA may have resource-level access without enumeration permissions.
 
+`auth login` validates SATs the same way. PATs are verified with `GET /ng/api/accounts/{accountID}`, but that endpoint needs account-view permission, which service accounts are rarely granted — so for SATs login calls `POST /ng/api/token/validate` instead. A 403 from that endpoint means the service account is disabled or has no access to the account at all; `--no-validate` writes the profile without the check.
+
 ---
 
 ## Commands
diff --git a/modules/core/auth/login.go b/modules/core/auth/login.go
index 4f3e636..7137fc2 100644
--- a/modules/core/auth/login.go
+++ b/modules/core/auth/login.go
@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"os"
 	"regexp"
+	"strings"
 	"time"
 
 	"github.com/harness/cli/pkg/auth"
@@ -230,11 +231,25 @@ func fetchRegistryURL(apiURL, token, accountID string) (string, error) {
 	return parsed.Data.RegistryURL, nil
 }
 
-// validateToken calls GET /ng/api/accounts/{accountID} to verify the token.
+// validateToken verifies the token against the API. PATs are checked by reading the account
+// resource; SATs use the token introspection endpoint instead, since service accounts are
+// rarely granted account-view permission and would otherwise fail with a 403.
 func validateToken(apiURL, token, accountID string) error {
 	c := &http.Client{Timeout: 10 * time.Second}
-	url := fmt.Sprintf("%s/ng/api/accounts/%s?accountIdentifier=%s", apiURL, accountID, accountID)
-	req, err := http.NewRequest("GET", url, nil)
+	isSAT := auth.TokenType(token) == auth.TokenKindSAT
+
+	var req *http.Request
+	var err error
+	if isSAT {
+		url := fmt.Sprintf("%s/ng/api/token/validate?accountIdentifier=%s", apiURL, accountID)
+		req, err = http.NewRequest("POST", url, strings.NewReader(token))
+		if err == nil {
+			req.Header.Set("Content-Type", "text/plain")
+		}
+	} else {
+		url := fmt.Sprintf("%s/ng/api/accounts/%s?accountIdentifier=%s", apiURL, accountID, accountID)
+		req, err = http.NewRequest("GET", url, nil)
+	}
 	if err != nil {
 		return fmt.Errorf("building validation request: %w", err)
 	}
@@ -253,6 +268,9 @@ func validateToken(apiURL, token, accountID string) error {
 	case 401:
 		return fmt.Errorf("token rejected (401) — check that your API token is valid\n\nTip: run 'harness auth profiles' to see available profiles, then retry with --profile <name>")
 	case 403:
+		if isSAT {
+			return fmt.Errorf("service account token rejected (403) — the service account may be disabled or lack access to this account\n\nTip: pass --no-validate to write the profile anyway, then run 'harness auth status' to see which scopes are reachable")
+		}
 		return fmt.Errorf("token valid but access denied (403) — check account ID or RBAC permissions")
 	default:
 		// Try to extract a message from JSON
diff --git a/modules/core/auth/login_test.go b/modules/core/auth/login_test.go
index a8a2d42..ee82a52 100644
--- a/modules/core/auth/login_test.go
+++ b/modules/core/auth/login_test.go
@@ -5,6 +5,7 @@ package auth
 
 import (
 	"encoding/json"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -370,6 +371,77 @@ func TestValidateToken(t *testing.T) {
 	}
 }
 
+// satToken is a syntactically valid SAT whose account segment is "acctid".
+const satToken = "sat.acctid.tokenid.secret123"
+
+func TestValidateToken_endpointByTokenKind(t *testing.T) {
+	tests := []struct {
+		name       string
+		token      string
+		wantMethod string
+		wantPath   string
+		wantBody   string
+	}{
+		{
+			name:       "SAT uses token introspection",
+			token:      satToken,
+			wantMethod: "POST",
+			wantPath:   "/ng/api/token/validate",
+			wantBody:   satToken,
+		},
+		{
+			name:       "PAT uses account lookup",
+			token:      validToken,
+			wantMethod: "GET",
+			wantPath:   "/ng/api/accounts/acctid",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var gotMethod, gotPath, gotBody string
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				gotMethod, gotPath = r.Method, r.URL.Path
+				b, _ := io.ReadAll(r.Body)
+				gotBody = string(b)
+				w.Write([]byte(`{"data":{}}`))
+			}))
+			defer srv.Close()
+
+			if err := validateToken(srv.URL, tc.token, "acctid"); err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if gotMethod != tc.wantMethod {
+				t.Errorf("method = %q, want %q", gotMethod, tc.wantMethod)
+			}
+			if gotPath != tc.wantPath {
+				t.Errorf("path = %q, want %q", gotPath, tc.wantPath)
+			}
+			if gotBody != tc.wantBody {
+				t.Errorf("body = %q, want %q", gotBody, tc.wantBody)
+			}
+		})
+	}
+}
+
+func TestValidateToken_SAT403MentionsServiceAccount(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(403)
+	}))
+	defer srv.Close()
+
+	err := validateToken(srv.URL, satToken, "acctid")
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), "service account token rejected (403)") {
+		t.Fatalf("error = %q, want the service-account-specific 403 message", err)
+	}
+	if !strings.Contains(err.Error(), "--no-validate") {
+		t.Fatalf("error = %q, want a --no-validate escape hatch in the hint", err)
+	}
+}
+
 func TestValidateToken_unreachableServer(t *testing.T) {
 	// Use a server that is immediately closed so the HTTP request fails.
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))