Garrard donated roughly £1.5 million ($2.1 million as of today) before Corbyn became leader of the party.
While friction between Jewish advocacy groups and Corbyn has existed nearly since the start of his reign, the latest confrontation began when a 6-year-old Facebook posting was brought to public attention last month by a Labour Party lawmaker who is Jewish.
It follows a report by The Sunday Times which found that 12 senior Labour staff and the shadow chancellor John McDonnell were members of groups where attacks on Jewish people, including Holocaust denial, were found to be routine.
She was replaced on the leadership committee by actor-comedian Eddie Izzard, who on Sunday acknowledged Labour's rift with Britain's Jews.
One of Labour's biggest private donors has said he no longer feels "any affinity or connection" with the party, and accuses its leadership of failing in its response to "the most blatant acts of antisemitism".
May's message comes at the end of a week in which outrage among the Jewish community and its supporters over antisemitic incidents in and surrounding the Labour Party bubbled to the surface, with over 2,000 people gathering outside the United Kingdom parliament to challenge Labour Party leader Jeremy Corbyn's perceived failure to tackle the issue.
She was forced to stand down from her position on Labour's disputes panel on Wednesday, after she sent an email calling for a council candidate accused of Holocaust denial to have his suspension lifted.
One post on a Facebook group called Jeremy Corbyn True Socialism said of Berger, "Get rid of this cancer", while another called her "a vile Zionist".
"The Labour Party is committed to challenging and campaigning against anti-Semitism in all its forms".
'But a lot of these people did not even realise they were members of these groups.
He said his decision was due to his "dismay and foreboding" over the way the party's leadership has conducted itself.
Mr Byrne said Mr Corbyn now needed to make good his promise to Jewish leaders to tackle the issue, pointing to the backlog of around 70 cases of anti-semitism still to be dealt with.
Corbyn had been enjoying a relative lull after an nearly constant media spotlight on cases of alleged anti-Semitism within Labour's ranks through 2016 and 2017.
"It is fine when you hear two or three cases a year".
British Labour Party leader Jeremy Corbyn is facing growing criticism over his handling of reported anti-Semitism among some of his supporters.