David Tennant, shown July 3, 2007, in London, is to star in the U.S. comedy Rex Is Not Your Lawyer. (Anthony Harvey/Associated Press)

Scottish actor David Tennant is moving out of the cosy confines of the Tardis time machine and into U.S. television comedy.

Tennant, the lead actor in BBC's Dr. Who, is to play a Chicago lawyer who coaches his clients to represent themselves in court in the new NBC sitcom Rex Is Not Your Lawyer.

The comic role has Tennant playing a lawyer so prone to panic attacks he cannot be relied on in the courtroom.

Tennant has played Dr. Who in the sci-fi series for the past five years but announced he would leave the show last year.

"I think it's better to go when there's a chance that people might miss you, rather than to hang around and outstay your welcome," he said.

Tennant is known in Britain for roles in TV dramas such as Blackpool and Casanova, and he also starred in Harry Potter and the Goblet of Fire. He played Hamlet with the Royal Shakespeare Company earlier this year.

The U.S. comedy is to be directed by David Semel, who worked on episodes of House and Heroes.