Harris will play the main stage on Saturday 24 May ahead of first-day headliners Coldplay, station bosses announced.
Harris declared: “I would feel really left out to not be there, so I’m well excited.”
Around 50,000 revellers are expected to descend on Glasgow Green for the weekend-long event, described as Europe’s largest free music festival.
More than 50 artists and bands will be performing across the event’s three stages.
Boy band One Direction are set to open the event, with Bastille, Pharrell Williams, Jake Bugg, Lily Allen and Ed Sheeran also billed to perform on the main stage on the Saturday.
US pop star Katy Perry will headline the final night, while Kings Of Leon, The Vamps, John Newman, Rita Ora, The 1975, Tinie Tempah and Paolo Nutini are also set to play the main stage on Sunday 25 May.