Greenstein, a Jewish anti-Zionist, was removed as part of the party's effort to combat antisemitism among its members.
"His continued membership is at complete odds with our collective values of solidarity, tolerance and respect," the party's chair of its Jewish Labour Movement, Ivor Caplin, said.
Greenstein has repeatedly made controversial and damning statements, particularly concerning Jews and Israel. He has used the term "Zio idiots" to describe those who criticize him, and has compared Israeli Jews to white South Africans who propagated apartheid.
Jews in Israel are like Whites in S Africa - privileged - that's y they want 2 convert Jews converted en masse in Nazi occupied Europe https://t.co/gavhVgJk5j— Tony Greenstein (@TonyGreenstein) September 16, 2017
He has also referred to Jews as Nazis and consistently calls Jews "zios," a derogatory term for Zionist.
On his blog, Greenstein maintained that he was expelled not because of his antisemitic remarks, but because he is against Zionism.
"The allegations of ‘anti-Semitism’ in the Labour Party have nothing to do with anti-Semitism and everything to do with opposition to the racist creed of Zionism and support for the Palestinians," he wrote.
He also referred to Caplin as a "junior war criminal," but did not expand on this.