The Emmy Award-winning actress will star in the six-part series produced by ITV Studios for BBC One, which will air later this year.
Game of Thrones actor Ciaran Hinds and Anna Chancellor will also have roles in the series, alongside James Cosmo, Saskia Reeves, Sara Vickers, Jack Greenlees, Jamie Michie, Mark Cox, Kate Donnelly and Andrew Rothney.
Douglas Henshall will return as Di Jimmy Perez, alongside series regulars Alison O'Donnell, Steven Robertson, Julie Graham and Mark Bonnar.
The third series will centre around the disappearance of a young man on a ferry crossing from Aberdeen to Lerwick.
Hinds said of his role: "I'm looking forward to locking swords with Douglas Henshall and working against the stunning backdrop of Shetland.
"I came to Scotland a lot in the '70s and '80s in various theatre productions - and,