Prince, the Eagles and Morrissey are among the previously confirmed headline acts for the event, which will take place between July 1 and 3 in Paddock Wood, Kent.
Hot Chip and Aloe Blacc will play the newly added Sunday show. Further acts confirmed to play the third day include Eliza Doolittle, Fenech Soler, The Pierces and The Go! Team.
"Going to a three-day event in year four is a great achievement for the festival. We are very pleased with our lineup and are looking forward to the festival," organiser Vince Power said in statement.
The Hop Farm festival will play host to hundreds of acts over four stages during the weekend, while maintaining its no sponsorship, no branding policy.
Tickets for the festival are on sale now.