Chairman Pat Brady has faced pressure to resign ever since he said he personally supported legalizing gay marriage, and survived a coup attempt from anti-gay marriage Republicans last month with the help allies of Sen. Mark KirkMark KirkGiffords, Scalise highlight party differences on guns Stale, misguided, divisive: minimum wage can't win elections Immigration critics find their champion in Trump MORE (R-Ill.). Kirk recently came out in support of same-sex marriage, and Illinois's state legislature is currently considering a bill that would legalize it in the state.

Brady's departure comes as Illinois Republicans attempt to rebuild the state party after a rough 2012, when they lost four House seats after redistricting and slipped further into the minority in the statehouse. The state party has long had tensions between social conservatives and the centrists who tend to do better in general elections in the state.