Lissack will join up with the Irish trio to make them a four-piece for the gig run, set to kick off in Southampton on April 19.
Lissack has been involved in side-project Pin Me Down while Bloc Party frontman Kele Okereke has been working on solo material since the band wound down last year.
“As soon as they called me I was really excited,” Lissack said. “I guess the only weird part would be spending so much time with people I don’t really know. I’m not sure how that will work out, but we seem to have got on well so far.”
See the new issue of NME, out tomorrow (March 17), for a full interview with Lissack in which he discusses how he was once in an Ash covers band and his thoughts on when Bloc Party will return from their break.
Ash will play:
Southampton University (April 19)
Cambridge Junction (20)
Norwich Waterfront (21)
Birmingham Irish Centre (23)
Leeds Metropolitan University (24)
O2 Academy Newcastle (25)
O2 ABC Glasgow (27)
Manchester Academy 2 (28)
O2 Academy Bristol (30)
Brighton Concorde (May 1)
O2 Academy Oxford (2)
London Electric Ballroom (4)