Iraq's main Sunni Arab political party, the Accordance Front, has said it is ending its boycott of parliament.
Mahmoud Mashhadani has been reinstated as speaker, his bloc says
The 44-member group walked out after one of its members was ousted as parliamentary speaker.
The group's return comes two days after the political bloc allied to Shia cleric Moqtada Sadr said it was ending its own boycott of parliament.
The 30 Sadrists said they had decided to return after the government agreed to rebuild a bombed Shia shrine.
The Accordance Front said Mahmoud Mashhadani has been reinstated as speaker.
The boycotts of the 275-seat parliament by the Sunni and Shia groups have hampered the passage of important laws demanded by the US Congress.
Mr Mashhadani has been surrounded by controversy during his tenure.
His has been accused of ordered his bodyguards to beat a fellow MP, and has been criticised for calling anti-US insurgents "heroes" and slapping another Sunni MP in the face.