In his resignation letter, Barrow and Furness MP John Woodcock said Mr Corbyn would pose a “clear risk to UK national security as prime minister”.
And he said that, under Mr Corbyn, Labour was no longer “the broad church it has historically been” and there was little chance of returning it to an “inclusive, mainstream electoral force”.
Mr Woodcock, 39, had been sitting as an independent since having the Labour whip withdrawn in April pending investigation of an allegation of sexual harassment.
He denies allegations over supposedly inappropriate texts and emails to a former female staff member between 2014 and 2016.
In his resignation letter obtained by the North-West Evening Mail, he dismissed the party’s disciplinary process against him as “rigged” and said there was “clear evidence that the process has been manipulated for factional purposes”.
He accused Mr Corbyn of personally refusing to appoint an independent investigator to rule on his case.
A Labour spokesman said: “Jeremy thanks John for his service to the Labour Party.”
A former aide to Gordon Brown during his time as prime minister and shadow transport minister under Ed Miliband, Mr Woodcock has been one of the harshest internal critics of Mr Corbyn’s leadership of Labour.
He clashed with Mr Corbyn over his stance on nuclear weapons and anti-Semitism.
And in 2017 he stood for re-election in the Cumbria seat he has represented since 2010, but said he did not believe Mr Corbyn was fit to serve as prime minister and would not countenance voting to put him into 10 Downing Street.