The by-election was called following the death in August of Councillor Annie Gallop, who had served on the council for more than a decade. Labour's Molly Hartill secured 46.7% of the vote, a 10.3% increase from the party's share in May. Green Party candidate Sonia Winifred came second, with Liberal Democrat Christopher French in third.
Posting on X, Ms Hartill wrote: 'SO so proud to be elected as the @LambethLabour Cllr for Myatt's Fields. It's been a local campaign focussed on local issues and hope. I'm so excited to represent Myatt's on @lambeth_council and carry on the work of our brilliant late colleague, Annie.'
Fellow Labour councillor Dominic Lynch added: 'I could not be happier for the people of Myatt's Fields, what a champion they have in Molly!'
The Lambeth result came a day after Labour's Sagal Abdi-Wali won the Holborn and St Pancras parliamentary by-election with 47% of the vote, taking the seat formerly held by retiring Prime Minister Sir Keir Starmer. Ms Abdi-Wali declared the victory a win for 'hope' over fear and division.
The results provide fresh evidence of a 'Burnham bounce', with Labour enjoying an upturn in London polls since Andy Burnham succeeded Sir Keir Starmer as Prime Minister. There has been a dramatic turnaround for the party in the capital since the disastrous local elections earlier this year, which were partly responsible for Sir Keir stepping down.
Meanwhile, Reform has lost vote share in 10 of the 11 London council by-elections since May.