Addressing the Jewish Labour Movement’s (JLM) conference on Sunday, Sir Keir said: “Let me assure you, we will never let antisemitism sneak back into the Labour Party under cover.
“I see no greater cause in my leadership than this. This is my role.”
It came as Sir Keir announced that ex-MP Luciana Berger would lead a review of the party’s mental health strategy, four years after she quit Labour blaming “a “sea of cases” of antisemitism.
She rejoined Labour as a member last year, and her appointment to the key role was announced on Sunday.
Ms Berger claimed that Labour had “turned a significant corner” under Sir Keir’s leadership.
The former MP, who served as a shadow health minister between 2013 and 2016, will present recommendations ahead of the next election on how Labour should fulfil its plan to tackle mental illness.
It is another sign of progress in Sir Keir’s drive to “tear out antisemitism” from the “roots” of the Labour Party.
Addressing JLM members, Sir Keir said he had “dragged [the] party away from that abyss”, adding that he would “never let Britain go anywhere near it either”.
“This country will be safe for you and your children,” he promised.
Addressing Israel’s war in Gaza, sparked by Hamas’s 7 October attacks, Sir Keir said British antisemitism was not “born the day after” the killing spree.
“But nonetheless, after October the 7th we can all see that it’s taking a new shape,” he added.
And after a series of high-profile marches across the country in protest at Israel’s bombardment of Gaza, he addressed Jews who “can see hate marching side by side with calls for peace”.
“We understand that to be targeted for who you are, and attacked for things beyond your control, for your children to be afraid to walk the street or go to school, is the greatest anxiety that a parent or a community can face,” Sir Keir said.
In a warning about the future of the Conservative Party after the next election, he said he was “worried” about where it might go.
Right-wing Tories have used increasingly divisive language in recent months, and with a leadership contest expected if the Conservatives lose power, Sir Keir suggested there could be a further lurch to the right.
“I worry about where it might go, because the politics of division don’t help the Jewish community, and they’ve never helped the Jewish community,” he said.
Taking aim at Rishi Sunak and other senior Tories for engaging in culture wars, he warned that divisive politics “can easily boil over”. “I’m not sure the Tories can be trusted on that any more... I don’t know if they see the consequences,” he added.
Accepting her new role, Ms Berger said she was “delighted to be back working with my party”.
Ms Berger, who stood as a Liberal Democrat in the 2019 election and lost her seat, said: “Millions of people are experiencing poor mental health without the necessary support to recover.
“The absence of a proper plan to address the causes of poor mental health requires urgent attention. Labour’s commitment to deliver a cross-government long-term strategy to tackle mental ill-health is an important step towards gripping this issue, and I am really excited to be leading this work.”