The Love Actually star went door to door in Walton-on-Thames with the party’s candidate Monica Harding, speaking to residents and urging them to vote tactically to defeat the Conservative incumbent.
Pro-Brexit Mr Raab has a majority of 23,298 in the Esher and Walton constituency, which voted to remain in the 2016 referendum.
Grant has been on the general election campaign trail supporting a number of prospective parliamentary candidates and advocating tactical voting to prevent a Tory majority.
His political activism has attracted a backlash from social media users, prompting him to face-down trolls recently by posting his own mugshot on Twitter.
Grant told a small rally on Saturday that it was not a “normal general election”.
He added: “We are not in a normal general election here, we are on the edge of a proper abyss in British history.
“This is very very frightening, the [Conservative] party has been captured by an extreme right-wing coup.”
The Notting Hill actor urged people to vote tactically to ensure the Conservatives did not win the election.
He told residents that a Tory victory would lead to the “catastrophe” of a no-deal Brexit.
Stopping at one home for a cup of tea and speaking to neighbours, Grant urged one woman who said she had always voted Labour not to vote with her heart.
He added: “We have the voting system we have, right now we can’t change it.
“That means if you vote with your heart your vote is gone, Dominic Raab gets in and all the catastrophe that follows from that.”
Grant has previously campaigned alongside Labour and independent candidates in other marginal seats.
He was recently heckled by a group of anti-racism protesters as he campaigned for Labour in Chingford.
The actor has previously revealed he would be voting for the Liberal Democrats in his own constituency because they are the nearest challengers to the Conservatives.