The remaining members - Hayley Williams, Taylor York and Jeremy Davis - will continue as a three-piece.
The band's website posted a new announcement, which began: "Over the past six years, our band has been through some of the most intense and incredible experiences of our lives. None of these things have been without trial."
It continued: "A couple of months ago, Josh and Zac let us know they would be leaving the band after our show in Orlando last Sunday. None of us were really shocked. For the last year it hasn't seemed as if they wanted to be around anymore.
"We want Josh and Zac to do something that makes them happy and if that isn't here with us, then we support them finding happiness elsewhere. But we never for a second thought about leaving any of this behind."
They reassured fans that they will continue without the drummer and guitarist, adding that they have big plans for 2011.
"We have some amazing things lined up for next year starting with our tour in South America. We are still coming to you and we are excited about who we are bringing with us! The tour is still on and we can't wait to see you all."