The party leader pledged to safeguard Britain's future outside the EU and ruled out rejoining any of the main Brussels institutions.
He said going back to the customs union, single market or allowing the return of free movement were all off the table.
In an exclusive interview with the Sunday Express, Sir Keir said the days when he was perceived as a Brexit blocker are over.
He insisted he wants to rebuild Britain's future as a fully independent nation.
Sir Keir declared: "Let me be really clear about Brexit. There is no case for going back into the EU and no case for going into the single market or customs union. Freedom of movement is over. There will be no return to that, either.
"What we want to do is make Brexit work." Riding high, 20 points ahead of Rishi Sunak's Tories in the polls, the buoyant but grounded ex-lawyer is on a mission to win back the trust of Leave voters who jumped ship in the 2019 election.
He also removed a second stumbling block to power by revealing far-Left former leader Jeremy Corbyn has almost no hope of standing as a Labour candidate while he is in charge.
And in a further shift of party positioning, he said the shortage of skilled workers must be remedied by training Britons, and not by importing cheaper labour.
Sir Keir said: "We can't rely on bringing in talent from abroad." However, he also revealed he supports a points-based immigration system so qualified people can come to the UK when there is a specific shortage of skilled workers, such as the dearth of HGV drivers this year.
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