Eric Joyce, the MP found guilty of drunkenly headbutting a rival politician in the House of Commons bar, has resigned from the Labour Party.
Delivering a personal statement in the Commons on Monday afternoon the Falkirk West MP said he apologised "without reservation" for his violent conduct during a drunken frenzy in the Palace of Westminster bar.
"Members will be aware of the events in the Strangers Bar on 22 February," he said. "During which the standard of my conduct fell egregiously below what is required of a member of this House and of anyone anywhere."
Joyce was suspended from Labour following the incident last month and he told the Commons he had now quit the party.
"I would like to express my thanks to MPs on both sides of this House and the other place who have contacted me to express concern, however undeserved on my part," he said.
"Clearly I have a number of personal issues to address," he added. "I have today tendered my resignation as a member of the Labour Party."
Last week Joyce was given a 12-month community order banning him from entering pubs and licensed premises for three months.
He was also fined £3,000 by Westminster Magistrates' Court and ordered to pay £350 to each of his victims.
Joyce admitted attacking four people in Parliament's Strangers Bar in February, including headbutting Tory MP Stewart Andrew.
Speaking outside the court on Friday, Joyce said he intended to stay in parliament until the 2015 general election but expressed "personal shame" at his actions.
"I've been duly punished today. I've been lucky to avoid prison. I'm very ashamed, of course," he said.
Joyce told the Commons today that he appreciated the "considerable grace" with which his victims had displayed in their public comment.