Labour MP Jared O’Mara who was suspended over sexist and homophobic comments has quit the party, saying he had been "made unfairly to feel like a criminal".
Mr O'Mara said he had experienced "little to make me feel welcome, understood and accepted" in the party in the last year after his past behaviour came to light.
The Sheffield Hallam MP had the whip withdrawn last year after a series of postings, many dating back over a number of years, came to light, but was readmitted earlier this month after receiving a formal warning.
In an open letter to his Yorkshire constituents posted on his website on Thursday, he said he did not feel he had been listened to or faced a fair investigation.
He wrote: "I am of the opinion that the Labour Party no longer shares my commitment to the true definition of equality and compassion.
"There is no doubt that I made mistakes as a young man using distasteful language as a clumsy attempt at satire and sarcasm online. But that does not mean that is who I am today."
Mr O'Mara, who took his seat from ex-Lib Dem leader Nick Clegg in the 2017 election, had not even made his maiden speech in the Commons when comments emerged that he had made in his early 20s, including inviting the band Girls Aloud to an orgy and joking about the musician Jamie Cullum being "sodomised to death".
The party's national executive committee disputes panel ruled earlier this month that the case did not meet the threshold required to be referred for expulsion but that he should undergo mandatory training.
On Tuesday he said he had made three suicide attempts at the height of the furore.
In his letter, Mr O'Mara suggested he will not step down as an MP, saying "I might be leaving Labour but I am still at your side", and offering constituents help with casework.
Describing himself as "the first autistic MP in our history", he wrote: "I didn't commit any crimes, yet I have been made unfairly to feel like a criminal.
"Nobody should be made to feel ashamed for mistakes they make when they are young."
He added: "I would be lying to those of you whom I represent, and those close to me like my parents and sister respectively, if I continued under the pretence that I feel there is a place of acceptance and empathy for me as a working-class, underprivileged disabled man within the Labour Party.
"I have experienced little to make me feel welcome, understood and accepted during this last year."
A Labour Party spokesman said: "We're disappointed Jared has decided to resign from Labour after we won the Sheffield Hallam seat from Nick Clegg and the Lib Dems last year.
"We wish him well for the future."