Tom Watson has called Luciana's departure from Labour over antisemitism "the worst day of shame in the party’s 120-year history".
The party's deputy leader said Ms Berger was "a pregnant young MP bullied out of her own party by racist thugs".
The Liverpool Wavertree MP faced motions of no confidences from her local Labour party, over her criticisms of Jeremy Corbyn's failure to tackle Jew-hate within the party.
She was among eight MPs to quit Labour last week, citing she had come to "come to the sickening conclusion is institutionally antisemitic".