diff --git a/cli/src/commands/workspace/forget.rs b/cli/src/commands/workspace/forget.rs
index 72be660d8..bc119179d 100644
--- a/cli/src/commands/workspace/forget.rs
+++ b/cli/src/commands/workspace/forget.rs
@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use clap_complete::ArgValueCandidates;
 use itertools::Itertools;
 use jj_lib::op_store::WorkspaceId;
 use tracing::instrument;
@@ -19,6 +20,7 @@ use tracing::instrument;
 use crate::cli_util::CommandHelper;
 use crate::command_error::user_error;
 use crate::command_error::CommandError;
+use crate::complete;
 use crate::ui::Ui;
 
 /// Stop tracking a workspace's working-copy commit in the repo
@@ -29,6 +31,7 @@ use crate::ui::Ui;
 pub struct WorkspaceForgetArgs {
     /// Names of the workspaces to forget. By default, forgets only the current
     /// workspace.
+    #[arg(add = ArgValueCandidates::new(complete::workspaces))]
     workspaces: Vec<String>,
 }
 
diff --git a/cli/src/complete.rs b/cli/src/complete.rs
index 997c89085..d138dc432 100644
--- a/cli/src/complete.rs
+++ b/cli/src/complete.rs
@@ -271,6 +271,27 @@ pub fn operations() -> Vec<CompletionCandidate> {
     })
 }
 
+pub fn workspaces() -> Vec<CompletionCandidate> {
+    with_jj(|mut jj, _| {
+        let output = jj
+            .arg("--config-toml")
+            .arg(r#"templates.commit_summary = 'if(description, description.first_line(), "(no description set)")'"#)
+            .arg("workspace")
+            .arg("list")
+            .output()
+            .map_err(user_error)?;
+        let stdout = String::from_utf8_lossy(&output.stdout);
+
+        Ok(stdout
+            .lines()
+            .map(|line| {
+                let (name, desc) = line.split_once(": ").unwrap_or((line, ""));
+                CompletionCandidate::new(name).help(Some(desc.to_string().into()))
+            })
+            .collect())
+    })
+}
+
 /// Shell out to jj during dynamic completion generation
 ///
 /// In case of errors, print them and early return an empty vector.
diff --git a/cli/tests/test_completion.rs b/cli/tests/test_completion.rs
index 5ad32bd15..3bd1fff78 100644
--- a/cli/tests/test_completion.rs
+++ b/cli/tests/test_completion.rs
@@ -446,3 +446,29 @@ fn test_operations() {
     let stdout = test_env.jj_cmd_success(&repo_path, &["--", "jj", "op", "undo", "5b"]);
     insta::assert_snapshot!(stdout, @"5bbb4ca536a8	(2001-02-03 08:05:12) describe commit 968261075dddabf4b0e333c1cc9a49ce26a3f710");
 }
+
+#[test]
+fn test_workspaces() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "main"]);
+    let main_path = test_env.env_root().join("main");
+
+    std::fs::write(main_path.join("file"), "contents").unwrap();
+    test_env.jj_cmd_ok(&main_path, &["describe", "-m", "initial"]);
+
+    test_env.jj_cmd_ok(
+        &main_path,
+        // same prefix as "default" workspace
+        &["workspace", "add", "--name", "def-second", "../secondary"],
+    );
+
+    let mut test_env = test_env;
+    test_env.add_env_var("COMPLETE", "fish");
+    let test_env = test_env;
+
+    let stdout = test_env.jj_cmd_success(&main_path, &["--", "jj", "workspace", "forget", "def"]);
+    insta::assert_snapshot!(stdout, @r"
+    def-second	(no description set)
+    default	initial
+    ");
+}