Portsmouth South MP Mike Hancock has resigned his membership of the Liberal Democrats the party has confirmed.
The move came after the veteran MP, who had already been suspended by the party, was forced publicly to apologise to a vulnerable woman constituent for making improper sexual advances.
In June Mr Hancock gave an "unreserved" apology at London's High Court over an "inappropriate and unprofessional friendship" with a single mother known as Annie, who had sought his assistance as her MP and local councillor.
Solicitors for the woman said the apology was part of a "confidential settlement" in which the "vulnerable woman", who suffers from mental health problems, brought a claim for damages against him.
A Lib Dem spokesman said Mr Hancock had quit before an internal party disciplinary hearing.
Lib Dem leader and Deputy Prime Minister Nick Clegg had previously called on Mr Hancock to resign his membership and said he had "no future" in the party.
A Lib Dem spokesman said: "I can confirm he has resigned from the party. "We have received a letter confirming his resignation. Obviously, there was due to be a disciplinary hearing imminently, so before that has happened he has resigned."
Under fire Portsmouth MP Mike Hancock is in hospital following calls for him to resign over harassment claims.
Mr Hancock's office said he has been in hospital since the end of last week and will remain so until at least the end of next week.
His offices in London and Portsmouth remain open as usual.
The Portsmouth South MP has been suspended from the Liberal Democrat party.
It follows a leaked report into alleged sexual impropriety with a female constituent.
He denies any wrong-doing but is facing a civil case brought by his accuser.
A retired naval commander, who's spent 15 years trying to get medals for a group of veterans, has begged the Prime Minister from his hospital bed to hand them out before it's too late.
Eddie Grenfel, 93, took part in the trecherous Arctic Convoys to support the Russian forces in World War Two.
More than 3,000 sailors died running a freezing gauntlet of German U-boats to keep Russia supplied.
Mike Hancock, Lib Dem MP for Portsmouth South, has written to Defence Secretary Philip Hammond and the Prime Minister calling for the matter to be treated as a priority. Fred spoke to him earlier.