MP Heidi Allen has announced she will not stand at the next election.
The member for South Cambridgeshire joined the Liberal Democrats earlier this month after quitting the Conservatives in February.
Ms Allen, 44, said she had suffered "utterly dehumanising" abuse and was "exhausted" by the "nastiness and intimidation" she had faced.
She was first elected in 2015 and announced her decision in a letter to her constituents.
Her announcement comes in the wake of Labour's announcement that it would back a December general election.
In the letter, Ms Allen said she had endured invasions of her privacy after Brexit had "broken our politics".
She said: "Nobody in any job should have to put up with threats, aggressive emails, being shouted at in the street, sworn at on social media, nor have to install panic alarms at home.
"Of course public scrutiny is to be expected, but lines are all too often regularly crossed and the effect is utterly dehumanising."
In August, a man was jailed for 24 weeks after he sent menacing tweets and a Facebook post to Ms Allen.
"While Parliament has been in purgatory, we have legislated for almost nothing, changed almost nothing and improved almost nothing," she added.
"I am heartbroken, but I know it is the right decision because I am no longer delivering the change that drove me into politics in the first place."
She said she felt it was important both Boris Johnson and Jeremy Corbyn were denied a majority in any upcoming election.
Ms Allen briefly became the leader of the fledgling Change UK earlier this year, but left after the party's failure to win any seats in the European elections.