The 'Many of Horror' rockers are "thrilled" at the prospect of performing at the spectacle - which is set to take place at Dores, near Inverness, Scotland between from June 8-10 - where they will be joined by Ed Sheeran, Mumford And Sons and Deadmau5 in what will be their first ever festival headline slot in Scotland.
The Scottish group - who last played at the Loch Ness festival three years ago - said: "We are thrilled to be returning to Rock Ness in June, and this time we'll be headlining.
"The location is amazing and the enthusiastic crowd made for a memorable experience in 2009, so we're counting down The Days until our return in 2012.''
Festival director Jim King is looking forward to an "extra-spectacular" Biffy Clyro perforamnce, and he is delighted to have secured the services of French electronic music duo Justice.
He explained: "It was only a matter of time before we got lucky and were able to welcome Biffy Clyro back to Loch Ness. Since their debut they've gone on to become one of the biggest rock bands in the UK and on home turf you know they're going to produce something extra-spectacular.
"Mumford And Sons. Wow. I am over the moon they agreed to play our show. They could have played anywhere but they chose The Highlands. It's going to be special.
"Justice is the act everyone has been asking us to book since we started the festival. French house music holds a special place at Rock Ness and these guys are simply the best."