The soul star, who made her name in The Supremes and is famous for hits including Baby Love, Stop! In The Name Of Love, I’m Coming Out and Upside Down, said it was “a dream come true” to be performing at the festival.
Next year’s event is a big one for Glastonbury as it marks the festival’s 50th anniversary.
The Sunday legends slot on the famous Pyramid Stage has become a firm tradition at the festival, often drawing the biggest crowd of the weekend.
Ross, 75, will follow in the footsteps of acts including Dolly Parton, Lionel Richie, Tom Jones and Dame Shirley Bassey, as well as Kylie Minogue, who performed an emotional set to a huge audience earlier this year.
Announcing her place in the 2020 line-up, the Motown singer tweeted: “This is a dream come true. To all the fans across the world, this is my tribute to you.
“I’m coming to Glastonbury, with love.”
Throughout her career, Ross has achieved 75 UK Top 40 singles as a solo artist and with The Supremes, and three number one albums as a solo artist, according to the Official Charts Company.
Festival organiser Emily Eavis said: “I am delighted to say that one of the all-time greats, the wonderful Diana Ross, is coming to Glastonbury to play the Sunday legend slot on the Pyramid next year.”
Sir Paul McCartney is rumoured to be headlining for the 50th anniversary celebrations next year, but has not been confirmed.
“I’m starting to think about whether I can or whether it would be a good thing,” the ex-Beatle has said.
All 135,00 tickets for Glastonbury’s 50th anniversary sold out in just over half an hour at the weekend, organisers said.