The independent MP for St Helens North has announced he will not run at the next general election.
Conor McGinn was suspended by Labour in December 2022 pending an internal party investigation into a complaint against him.
The nature of the complaint has not been made public.
Mr McGinn on Friday said he was stepping away from Westminster for health and family reasons.
In a letter posted to Twitter, he wrote: “As is well known I have had a number of health issues over the last year including a heart condition, all of which has had a significant impact on me and my family.
“I think it is therefore the right time for me and the right thing to do for my young family to step away from Westminster and start a new chapter in our lives, and therefore I do not intend to stand at the next General Election.”
He also referred to “mistakes” made, though he did not elaborate.
“Like everyone, I made mistakes and sometimes got it wrong, but I am very proud of what I have achieved and the good things I have done as an MP over my three terms,” he said.
“I am going to take some time off to fully recover from my ongoing health issues, and then I will continue to work hard for our fantastic community in St Helens and Newton-le-Willows until the next election.”
The representative for the Merseyside constituency had been a senior Labour MP until he was suspended from the party, forcing him to sit as an independent in the House of Commons.
He was a shadow minister without portfolio, playing a key role in preparing Labour for the next general election as deputy national campaigns co-ordinator.
At the time of his suspension, Mr McGinn said he had not been told the details of the complaint but believed it was “entirely unfounded”.
