The celebrity guests for David Letterman's final episodes of The Late Show have been announced and the lineup's impressive.

Over the next six weeks on US TV the likes of George Clooney, Robert Downey Jr and Bill Murray will appear across 28 instalments of Letterman's talk show before his final episode on Wednesday, May 20.

Scarlett Johansson, Michael Keaton, Steve Martin, Julia Roberts, Ray Romano, Jerry Seinfeld and John Travolta will take part in the upcoming shows.

Will Ferrell, Tina Fey, Paul Rudd, Bruce Willis, Tom Hanks and Oprah Winfrey are also booked to appear, with more names to be announced.

Celebrity guests for tonight's (April 13) show include Sarah Jessica Parker and 2015 Masters champion Jordan Spieth.

Guests for the remainder of this week will include Billy Crystal and Julie Chen (April 14), Michael J Fox and Amy Sedaris (April 15), Kevin James and Tracy Chapman (April 16), and Alec Baldwin and John Mayer (April 17).

Letterman announced in 2014 that he was retiring from The Late Show, and he has a career in late-night television dating back to 1982.

Stephen Colbert, who has signed a five-year deal with CBS, will succeed Letterman on September 8.