The MP said she was "sickened" by the tidal wave of anti-Jewish abuse in Jeremy Corbyn's party.
Allies warned that Labour "will be judged harshly" for allowing Ms Berger to be hounded out.
And Jewish groups said it was "desperately sad" to see her forced out by anti-Semitic bullies.
Ms Berger was one of seven MPs who quit Labour today to form a new "Independent Group" in Parliament.
Her decision to quit came after months of horrific abuse from far-left anti-Semites – which she claimed Mr Corbyn did nothing to stop.
She said: "I cannot remain in a party that I have today come to the sickening conclusion is institutionally anti-Semitic.
"We have only seen this situation – racism against Jewish people – get worse.
"The leadership has wilfully and repeatedly failed to address hatred against Jewish people within its ranks.
"I am leaving behind a culture of bullying, bigotry and intimidation."
Labour's deputy leader Tom Watson responded by saying: "They say anti-Semitism is a light sleeper – this is certainly a wake-up call for the Labour party.
"If someone like Luciana no longer believes there is a role for her in the Labour party, then many other colleagues I know will be asking themselves how they can stay.
"I confess I feared this day would come. And I fear now that unless we change, we may see more days like this."
Jonathan Goldstein, head of the Jewish Leadership Council, said: "Luciana Berger and others have been forced out of their political home by anti-Jewish bullies.
"This is desperately sad to see."
Marie van der Zyl, of the Board of Deputies, added: "In the light of the horrific abuse aimed at Jewish MPs, we stand in solidarity with all those who have been targeted."
Labour MPs who are staying in the party paid tribute to Ms Berger and warned the incident must be a warning to Mr Corbyn.
Wes Streeting said: "I have known Luciana Berger for 15 years. She is principled and courageous.
"The Labour party will be judged harshly, by voters and by history, for the hounding out of a Jewish woman in these circumstances."
Jess Phillips added: "If we cannot ask ourselves the question about why she was essentially constructively dismissed, let alone come up with the answers, we have little hope."
And Margaret Hodge, who has also suffered anti-Semitic abuse, said: "Luciana has faced outrageous abuse, threats and hatred from her local party as well as nationally.
"With no support from the leadership I understand why enough is indeed enough for her."
When Ms Berger was at university, she quit the National Union of Students claiming other committee members had bullied her.
In the past few weeks, some Labour activists in her Liverpool Wavertree seat threatened to deselect her.
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