The programme, which was one of the big winners at the TV Baftas at the weekend, will also feature James D'Arcy - who appeared in the films Cloud Atlas and Hitchcock - and Phoebe Waller-Bridge, from Bad Education and Blandings, for the second run.
Jane Featherstone, chief executive of Kudos and Broadchurch executive producer, said: "It's never easy to tempt actors back from Hollywood, and we feel privileged that James is joining us as a key part of our new story."
They join a cast which already includes David Tennant, Olivia Colman and Jodie Whittaker, who are all returning.
ITV's director of drama, Steve November, said: "We're delighted with the stellar cast assembled for the new series of Broadchurch. There's a real sense of heightened anticipation about what's to come, although we're desperate to protect the secrets of Broadchurch to avoid spoiling what happens next for the viewers."
Andrew Buchan, Arthur Darvill and Charlotte Rampling are also appearing in the drama which will return to the Dorset and north Somerset locations that featured in last year's run.
Writer Chris Chibnall said: "We're all thrilled about returning, especially given how supportive the whole community was last time. And if the community are able to keep our secrets as well as they did last time, we'll be ever so grateful."