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.