As previously announced, Bob Dylan will top the bill on Saturday, July 3, with support from Ray Davies, Laura Marling, Pete Doherty and others.
Organisers have now revealed that contrary to early suggestions, the festival will run for two days over three stages and Van Morrison will perform on Friday, July 2.
Founder Vince Power said: "We continue to have a great response from Hop Farm Festival fans and I am pleased to announce Van Morrison as the headline act for the Friday.
"And having Bob Dylan come out to do this exclusive performance on Saturday, I know this year will be one to remember."
Two-day tickets are now available for £110, with Friday tickets available for £45 and Saturday tickets for £65. Two-night camping passes are available for £25.
Neil Young headlined the first Hop Farm Festival in 2008, while last year's concerts saw performances from The Fratellis and Paul Weller.