Labour's shadow justice minister has quit its front bench and decided not to stand at the next general election.
Gloria De Piero, MP for Ashfield in Nottinghamshire, said she was unsure she could "sustain the energy and commitment of the last nine years".
She campaigned for Remain in a strongly pro-Brexit seat but does not support a second referendum.
In her speech to party members, she also hit out at a "lack of tolerance" in the Labour Party.
Shadow chancellor John McDonnell said her decision was "disappointing".
Speaking to members on Friday, Ms De Piero said: "I've had time to think about whether I can continue to give you all the energy and personal sacrifices that you need as a Labour champion for this constituency. You deserve the absolute best."
She added: "The Labour Party is made up of mostly good people who sometimes disagree on how to achieve good. There is nothing wrong with that. It's good and it's healthy and it should be welcomed.
"The lack of tolerance for different viewpoints in the Labour Party frankly worries me.
"We have to have respect for each other, even if we disagree, because we are all part of this Party."
She also said she received "grim" abuse on social media from people wanting to overturn the referendum result.
Earlier this month, Labour leader Jeremy Corbyn challenged the next Conservative leader to hold another referendum before taking the UK out of the EU, saying Labour would campaign for Remain.
In the EU Referendum 69.8% of voters in Ashfield voted Leave, on a turnout of 72.8%.
Ms De Piero has represented the traditionally safe Labour seat since 2010 but at the last election won by only a few hundred votes.
She continued: "This party is about a set of values not any individual and we would all do well to remember that.
"And while I'm at it, and it doesn't happen in Ashfield, but when I hear people being called right-wing in the Labour Party I find it utterly offensive.
"We are all left-wingers in this party - that is why we joined the Labour Party."
Mr McDonnell said he thought her speech was "lovely" but added: "We worked together as a team, [I'm] disappointed she's standing down, but we're a broad church in the Labour Party and we always will [be].
"If there's any evidence of intolerance, we've said to our MPs and members, let us know and we will take action."
Ms De Piero finished her speech by saying she "actually believes" in Brexit and would continue to campaign for a soft version of it, before inviting members back to her home for drinks and frozen pizza.
Correction 9th October 2019: This story has been updated to clarify that Ms De Piero said she was stepping down for personal reasons, not directly because of her views on a "lack of tolerance" within Labour.