Labour MP Liam Byrne has been found to have bullied a former member of staff and will be suspended from the Commons for two days.
The ex-Cabinet minister and MP for Birmingham Hodge Hill ostracised a former assistant after a minor office dispute, an investigation found.
Parliamentary Standards Commissioner Kathryn Stone said his behaviour was a “significant misuse of power”.
Mr Byrne said he had apologised and was “profoundly sorry”.
A number of other allegations relating to unreasonable behaviour by Mr Byrne and pressure to work excessive hours were not upheld, the report found.
The investigation was started almost two years ago after complaints were made by the MP’s former assistant David Barker to the Independent Complaints and Grievance Scheme (ICGS).
The recently-appointed body rules on bullying and sexual harassment complaints in the Commons and has now published its findings.
Mr Barker, a Labour party member who runs the food bank Baby Aid Birmingham, began working for Mr Byrne on a series of short-term contracts in April 2019, but lodged a complaint about him a year later. He agreed to be named in the report.
The independent expert panel report said: “The respondent’s [Mr Byrne’s] decision not to engage with the complainant following what he perceived to be acts of misconduct was not, as he argued, a reasonable HR strategy. It was bullying.
“He should, as he now accepts, have tackled any alleged misconduct through a proper disciplinary process not by ostracising the complainant.”
Speaking exclusively to BBC Midlands Today, Mr Barker said his experience had had a terrible impact on his mental health and had left him in fear of how he would be judged by future employers and within the party.
“When I contacted the ICGS I was devastated and increasingly isolated,” he said.
“I knew my job was over and nothing could be done to get it back, but now my career in Labour was at risk too because I had no reference.”
Mr Byrne, who has held his seat since 2004, served as a member of the Cabinet in Gordon Brown’s administration and was chief secretary to the Treasury from 2009-2010. Before that he served in a number of other ministerial jobs.
