Rosena Chantelle Allin-Khan was born in Tooting on 1 January 1977. Her Polish mother had been a singer in the Polish girl group Filipinki, who met her father, originally from Pakistan, while the band was on tour in London. The couple separated after having two children, and Allin-Khan's mother worked three jobs to support her and her brother.
She was educated at Trinity St Mary School. She studied medical biochemistry at Brunel University, funding her education through a series of part-time jobs. She went on to study medicine at Lucy Cavendish College, Cambridge, funded by scholarships.
After qualifying as a doctor, Allin-Khan worked at the Royal London and Homerton Hospitals. She went on to complete a Master's degree in public health. Following this, she spent many years working as a humanitarian aid doctor.
Prior to her election to the House of Commons, she worked as a junior doctor in the accident and emergency department at St George's Hospital in Tooting.
Allin-Khan was a councillor on Wandsworth Council for Bedford ward in Balham, and previously served as deputy leader of the council's Labour group.
Allin-Khan was selected as the Labour Party candidate for the Tooting constituency, after the seat was made vacant in May 2016 when the sitting MP, Sadiq Khan, resigned when he won that year's London mayoral election. Allin-Khan won the seat after a campaign which emphasised her working-class roots and Polish-Pakistani heritage. When the election results were announced, Allin-Khan read a tribute to Jo Cox, the Labour MP for Batley and Spen who had been murdered the day of the by-election.
On 9 October 2016, Allin-Khan was appointed shadow minister for sport. Allin-Khan retained her seat in the 2017 general election and the 2019 general election.