Labour’s Kim Leadbeater has narrowly won the Batley and Spen by-election following a bitter campaign.
After defeating her Conservative rival by just 323 votes, she said constituents had “rejected division” and “voted for hope”.
It means she will now represent the seat previously held by her sister Jo Cox, who was murdered there in 2016.
The result will ease pressure on Labour leader Keir Starmer after recent election defeats for his party.
Ms Leadbeater said the “vast majority” her conversations with voters during the campaign were about local rather than national issues.
Asked whether Sir Keir had been an asset or a problem for her, she said: “The focus of the campaign was very much listening to local people.”
The campaign in West Yorkshire was marred by acrimony, personal abuse and allegations of dirty tricks.
The contest was seen as an important test for leader Sir Keir, who welcomed Ms Leadbeater’s election as a “fantastic result”.
It had been reported he may have faced a challenge from his deputy Angela Rayner if the party lost another northern English constituency to the Tories.
In May, the Conservatives took Hartlepool, a once rock-solid Labour seat, winning a by-election there with a majority of almost 7,000 votes.
This came in addition to the loss by Labour of more than 300 councillors in England’s local elections.
In Batley and Spen Tory candidate Ryan Stephenson came second with 12,973, with former Labour and Respect MP George Galloway third with 8,264.
Speaking outside the count, Mr Galloway said he would apply to have the result set aside by the courts.
Sixteen candidates in total ran in contest. Turnout was 47.6%, with 37,786 verified ballots cast out of a total electorate of 79,373.
The contest was triggered after the previous Labour MP for the seat, Tracy Brabin, became West Yorkshire’s first elected mayor in May.