Labour's Rosena Allin-Khan has won the Tooting by-election in a contest overshadowed by the murder of MP Jo Cox.
Allin-Khan held the south London seat for Labour after London mayor Sadiq Khan stood down following his victory in the City Hall race in May.
The A&E doctor, who increased the Labour majority, used her acceptance speech to pay tribute to Cox as a "proud and passionate campaigner who will be desperately missed".
Allin-Khan increased Labour's majority to 6,357 over the Conservatives, up from the 2,842 secured by her predecessor in the general election last year.
In a sombre statement following her victory at Wandsworth Town Hall she referred to the "horrific events of yesterday and the shocking death of Jo Cox".
She added: "My thoughts and prayers are with Jo's husband and her children. She was a proud and passionate campaigner who will be desperately missed."
"Jo's death reminds us that our democracy is precious but fragile. We must never forget to cherish it," she said.
"Thousands of people voted today and we are all here in recognition of our democratic values."
A two-minute silence was observed during the by-election count as the murder of the MP for Batley and Spen in West Yorkshire cast a shadow over the process of electing the newest member of the Commons.
Paul Martin, the acting returning officer in the constituency, said the silence was to allow everyone involved in the count to "reflect upon this awful loss".