Described by the event’s organisers as “unstoppable forces in alternative rock on both sides of the Atlantic”, the pair will join the Red Hot Chili Peppers as well as Foals and Disclosure who are also co-headlining a day at the Bank Holiday Weekend extravaganza.
Biffy Clyro have risen through the ranks at the Leeds Festival and its sister event in Reading, having played various slots over the years including as headliners in 2013.
With a new album in the works the band will be aiming to build on their reputation as a top tier live act.
Fall Out Boy are no strangers to the event either with their 2013 performance attracting one of the biggest crowds in the festival’s history.
The band said: “It’s pretty surreal to hear we are going to be co-headlining Reading and Leeds.
“Reading and Leeds was our first real festival experience outside of the US and since the start we have buckled in and had an insane and memorable experience every time we have played.
“This is it, the big one for us and we are excited to be able to be a part of it.”
Festival chief Melvin Benn said: “This year really is a big one for Reading and Leeds.
“Five headliners across three days – it’s a first for us and the UK Festival scene.
“We’re always looking to give Reading and Leeds fans something new and this year isn’t going to disappoint.
“Biffy Clyro and Fall Out Boy are going to be incredible.”
Elsewhere there will be performances from synth-pop band Chvrches who are flavour of the month after two critically-acclaimed studio albums and also American rapper A$AP Rocky who is building on his recent number 1 on the US charts.
Also added to the line-up are London band The Vaccines, HAIM, The Wombats and The Dillinger Escape Plan.