Ian Austin has been the Labour MP for Dudley North since 2005, having previously been a councillor in the town.
The adoptive son of Czech Jewish refugees, he has been critical of attempts to tackle anti-Semitism within the party.
He was a minister for regional affairs under Gordon Brown.
The role came after a stint serving the former PM as a parliamentary aide.
He has also held several roles as a shadow minister, most recently for work and pensions in 2013.
He has described the decision to leave the party as the "hardest decision I have ever had to take".
A vocal critic of Jeremy Corbyn, he has said that with a "decent leader" Labour could be twenty points ahead in the opinion polls.
"I certainly don't believe he's fit to be prime minister", he told BBC WM shortly after quitting.
He retained his seat in the 2017 general election by the narrow margin of just 22 votes.
"This is one of the seats that Theresa May called the election to win", he said after his triumph.
He was investigated by Labour after a confrontation with party chairman Ian Lavery in the House of Commons in July 2018, which he called the party's code of conduct on anti-Semitism a "disgrace".
He had criticised the party's decision at the time not to adopt the International Holocaust Remembrance Alliance's "working definition" of anti-Semitism and all its examples - a move that was subsequently reversed.
The investigation was later dropped, with Mr Austin complaining that the party's handling of the case had been "appalling".
Although he backed Remain in 2016, he is opposed to the idea of holding another EU referendum.
This sets him apart from the eight Labour MPs who quit earlier this week to join the new breakaway Independent Group.
Mr Austin says he will not be joining the new group, although he has previously expressed sympathy with their aims.