Former Emmerdale actor Samuel Anderson is joining the show as Danny Pink - a teacher at Coal Hill School, which featured heavily in the original series.
The very first episode revolved around two of its teachers discovering one of their pupils, Susan, was actually the Doctor's grand-daughter and joining them on their adventures.
Viewers will also see Jenna Coleman, who plays Clara in the show alongside Peter Capaldi's Time Lord, working at the school.
Show supremo Steven Moffat said: "For the fourth time in Doctor Who history, Coal Hill School is coming to the aid of the Tardis. In 1963 teachers Ian Chesterton and Barbara Wright accompanied the first Doctor. These days it's the turn of Jenna Coleman as Clara Oswald.
"And very soon now, Sam Anderson as Danny Pink will be entering the world of the Doctor. But how and why? Answers are coming later this year in Peter Capaldi's first series of Doctor Who."
Anderson said: "I was so excited to join Doctor Who I wanted to jump and click my heels, but I was scared I might not come down before filming started.
"It's a quintessential part of British culture and I can't believe I'm part of it. It's an honour to be able to work alongside Peter Capaldi and Jenna Coleman and I can't wait to show people how my character becomes involved with such a fantastic duo".