Derek Hatton, who was expelled from Labour in the 1980s for being a member of Trotskyist group Militant, has been readmitted to the party.
The former Liverpool City Council deputy leader, 71, submitted a membership application in September.
It was officially approved this week – coinciding with the resignation of seven sitting MPs from the party, who cited antisemitism among reasons for their departures.
Mr Hatton rose to national attention in the 1980s for running an illegal council budget in Liverpool, demanding that Margaret Thatcher’s government made up the £30 million shortfall.
He was expelled in 1986 for belonging to Militant – a “party within a party”, which was found to have contravened Labour’s constitution groups with their own "Programme, Principles and Policy for separate and distinctive propaganda" ineligible for affiliation.
Under the leadership of Neil Kinnock, Labour’s National Executive Committee voted to expel him by 12 votes to six.
Mr Hatton, a prominent left-wing figure, has commented occasionally on the Labour Party’s antisemitism scandal, as well as on Israel.
In September, he suggested the party’s antisemitism crisis was “all to do with trying to remove Corbyn”, describing it as “an unholy alliance between the media, the Tories and many right wing MPs”.
Mr Hatton has also called for boycotts of “all sporting events with Israel”, accusing the country of “getting away with cold, calculated murder”.
