Former health minister Norman Lamb, who has served as the Liberal Democrat MP for North Norfolk since 2001, has said he will stand down at the next general election.
The 61-year-old does not hold a frontbench role within the party.
He told the Eastern Daily Press he has notified his party that he will not contest another election when one is called and said it felt like the "end of an era".
He said: "I absolutely don't want to stop working. but the things I'm passionate about are the things I can best promote outside parliament.
"And so everything built up through my work as a minister in mental health and learning disabilities and autism, I've got very strong views about how the system tramples over people's human rights."
He continued: "I think we are in a very sad and disturbing place in our politics.
"It feels like there are two camps.
"But I think the public expects politicians to rise above the fray and be willing to bring the country together again."
The Liberal Democrats have 14 MPs with 12 of them in frontbench jobs.
Changes were announced after Jo Swinson was elected as the party's leader last month.
The two Lib Dem MPs without frontbench roles are Mr Lamb and Sarah Wollaston, formerly of the Conservatives and Change UK and chairwoman of the Health Select Committee.
