Bradley Walsh revealed as Doctor Who companion
The trio will appear as the Doctor's "companions" Graham, Yasmin and Ryan in the next 10-week series slated for autumn 2018.
Broadchurch and Trust Me star Whittaker will take over in the Tardis from Peter Capaldi when the Time Lord regenerates as a woman for the first time after the Christmas special.
Actor, comedian and quiz show host Walsh was widely tipped to be the Doctor's new assistant, although further details of his role are yet to emerge.
A fan of the show for 50 years, he told the BBC: "I remember watching William Hartnell as the first Doctor. Black and white made it very scary for a youngster like myself.
"I was petrified, but even though I'd watch most of it from behind the sofa through my fingers, I became a fan...
"Am I thrilled to be part of this whole groundbreaking new dawn for the Doctor? Oh yes!"
Gill, who has appeared in Hollyoaks and Casualty, said she was "over the moon" to be appearing in the hit programme, while Cole, who has had roles in Star Wars and EastEnders, said he was excited to be "jumping in this Doctor Who universe".
Writer Chris Chibnall described them as "three of Britain's brightest talents".