Labour councillor and junior doctor Rosena Allin-Khan has been selected as the party's candidate for the Tooting by-election.
Born and raised in the area, Dr Allin-Khan works as an emergency doctor at St George's Hospital and is also deputy leader of Wandsworth Labour group.
Sadiq Khan's election as mayor of London last week triggered the fight for the south London seat.
Commenting on her selection, Labour leader Jeremy Corbyn said: "Labour has selected a great candidate to fight the Tooting by-election.
"Rosena Allin-Khan is a local doctor who is committed to defending local NHS Services."
Dr Allin-Khan describes herself as passionate about the NHS, her family and singing.
Expressing his delight at her selection, the new London mayor tweeted: "Congrats to good friend @DrRosena - our Labour candidate to be Tooting's next MP. Look forward to working together."
Mr Corbyn met with Dr Allin-Khan in Tooting following her victory where the two shared a conversation about football.
The Arsenal-supporting Labour leader was disappointed to hear Dr Allin-Khan is a Liverpool supporter.
Dr Allin-Khan told the Press Association she was "very excited" to challenge for the seat and praised the work carried out by her predecessor.
She said: "Sadiq Khan has left a fantastic legacy with his tireless work in he community in the last 11 years and I look forward to building upon all that he's done for community cohesion and all that he's done locally.
"I have a great track record in the area of campaigning tirelessly."
Dr Allin-Khan, who has provided emergency cover during the recent junior doctors' strikes, said she "welcomes" the recent talks between the British Medical Association and Health Secretary Jeremy Hunt.
She said: "It's the saddest day for doctors when they had to take the decision to go on strike, it's not something we took lightly."
Asked what she thought of the possibility of being challenged in the seat by former Labour MP George Galloway, Dr Allin-Khan said: "I have a lot of faith in my values as a Labour Party member. I believe in fairness, equality, social justice. These are the issues that I'm going to be standing for and that's what I'll say to you on that one.
"I'm not afraid to be open and honest about why I'm standing and anyone else obviously... that's how I feel," she added.