He said the event this weekend has the "best-ever" line-up, featuring bands ranging from One Direction to the likes of Katy Perry, Kings of Leon, Coldplay and Bastille.
Up to 50,000 revellers will attend the festival on Glasgow Green this Saturday and Sunday. A further 14,000 tickets for an additional dance event on Friday have also been given away.
Radio 1 DJs Annie Mac, Pete Tong, Zane Lowe and Danny Howard will all star in the George Square party to kick-start the weekend.
James, who hosts the 4pm-7pm Radio 1 show every weekday, said: "I really believe this is the best one ever for my tastes.
"Scottish crowds are always the most rowdy, they just love it when a big event comes into town, so with the Friday and the weekend nights it's just going to be a big party."
Coldplay are the headline act on Saturday while One Direction, Calvin Harris, Bastille, Pharrell, Jake Bugg, Lily Allen and Ed Sheeran will also perform that day.
Kings of Leon, The Vamps, John Newman, Rita Ora, The 1975, Tinie Tempah and Paolo Nutini will all perform on the Sunday, with Perry closing the festival.