Scottish Conservative MP Ross Thomson is to stand down after being accused of sexually assaulting a Labour MP in a Commons bar.
Mr Thomson said he had made the "hardest decision of my life" not to contest the seat for Aberdeen South at the general election.
Labour MP Paul Sweeney had said he reported Mr Thomson to Westminster's standards watchdog following the alleged incident last October.
Mr Thomson denies any wrongdoing.
But he said a number of "anonymous and malicious allegations" this year had made his life "a living hell".
Mr Thomson, 32, said: "This is a political smear and I will continue to fight to clear my name. I will see this investigatory process through to a conclusion.
"I have suffered a level of personal abuse that has affected my health, my mental wellbeing and my staff. It has been a level of abuse that I never imagined possible."
He added: "I have therefore made the most difficult decision that I could ever make. I have decided that I will stand down as the Scottish Conservative and Unionist candidate for Aberdeen South."
Mr Sweeney, who is the MP for Glasgow North East, told the Scottish Mail on Sunday he was left feeling "mortified" by the alleged attack in the Strangers' Bar at Westminster.
According to the paper, Mr Sweeney said he was "paralysed" with shock after Mr Thomson "groped" him in the bar.
He said the alleged incident took place in October 2018 after he had invited a group of his old Glasgow University friends for a tour of the Commons.
They later went to the Strangers' Bar for a drink where he claims they were interrupted by Mr Thomson, who was "drunk to the point where he was barely able to stand up".
Mr Thomson then allegedly grabbed at Mr Sweeney through his clothes.
Mr Sweeney said he repeatedly told Mr Thomson to stop touching him and asked him to leave.
The Labour MP said that he later asked for advice from the Women's Aid charity before approaching the Standards watchdog.
A House of Commons spokeswoman said: "Parliament's Independent Complaints and Grievances Scheme (ICGS) operates on the basis of absolute confidentiality.
"Therefore we cannot provide answers about any complaint that may or may not have been made."
In February, Mr Thomson was publicly accused of groping a man in the same Commons bar. The Tory MP also strongly denies any wrongdoing relating to that alleged incident.
Mr Sweeney said he was finally speaking out in public more than a year after the alleged assault because the investigations had "barely progressed".
A spokesman for the MP said: "This assault, which took place last October, was reported to the appropriate authorities after similar but entirely separate allegations were made by other men against Ross Thomson in February.
"Thomson's denials today fly in the face of what was witnessed by other MPs and visitors and show him to be utterly unrepentant."
Mr Thomson had issued a statement on Twitter on Sunday morning in which he strenuously denied Mr Sweeney's allegations, but insisted he would be a Tory candidate in the 12 December general election.
However, he later confirmed he was standing down from the job he "loved more than any other".
Mr Thomson, who has been an MP since 2017, said: "I always believed politics was about noble pursuits and doing what you believed to be best for your country.
"My experience is that our politics is now so poisonous that we will never attract good, honest and decent people in the first place.
"This has been without doubt the hardest decision of my life. I remain confident that the ongoing parliamentary standards process will find in my favour, and that these baseless claims will be shown up for what they are.
"As I have already said I will continue to explore all options available to me in response to the defamatory and damaging allegations made by Mr Sweeney."