The group went on hiatus in late 2009 so members Patrick Stump, Pete Wentz, Joe Trohman and Andy Hurley could pursue their own side projects.
"When we were kids the only thing that got us through most days was music," the group said in a message on its website Monday. "It's why we started Fall Out Boy in the first place. This isn't a reunion because we never broke up. We needed to plug back in and make some music that matters to us. The future of Fall Out Boy starts now."
The band's new CD, "Save Rock and Roll," is set for release May 6. The tour was to kick off Monday night with a sold-out gig in Chicago.
Notable deaths of 2014 [PHOTOS]
Bette Midler covers 'Waterfalls' by TLC