They will share the bill with Arctic Monkeys and Paolo Nutini, who have already been confirmed for the three-day festival at Balado in Kinross-shire.
Other big acts include Pharrell Williams, The Manic Street Preachers, Pixies, Ed Sheeran, Ellie Goulding, Jake Bugg, Rudimental and Disclosure.
Around 85,000 people are expected to flock to the annual music celebration, taking place from July 11-13. For the first time there will be a full day of performances on Friday starting at noon.
Simon Neil, singer and guitarist with fan favourites Biffy Clyro, said: "Genuinely T in the Park has shaped our lives in more ways than just our experiences of performing there.
"We wouldn't be here, doing this now, if it wasn't for playing T in the Park.
"To headline it finally is amazing - it just feels poetic to be headlining on our 10th time."
Calvin Harris said: "Last year was incredible, so I can't wait to be back this year. It's going to be amazing."
Festival director Geoff Ellis said it would be a "very special weekend".
He added: "Every year we ask our audience which acts they'd like to see at T in the Park, and we're thrilled to have some great acts joining us in Balado once again this summer."
Tickets go on sale at 9am on Friday from www.tin