Former foreign office minister Tony Lloyd has been elected as chairman of the Parliamentary Labour Party, ousting Ann Clwyd from the post.
Tony Lloyd had narrowly lost in the previous election
Mr Lloyd won 169 votes, while Ms Clwyd gained 156. She won last year's chair election with a margin of 11 votes.
Ms Clwyd is the PM's special envoy to Iraq and was seen by some backbenchers as being too close to Tony Blair.
As chairman, Mr Lloyd, an anti-war rebel, will be charged with ensuring ministers know of backbench concern.
In Tuesday's election, 92% of Labour MPs took part.
Ms Clwyd was said to be "extremely upset" following the vote in London.
Her election loss is the first time in about 25 years that a sitting chairman has been voted out.