Siddiq joined the Labour Party at the age of 16, later giving the NHS and the care her disabled father as the main reason.
She named former cabinet minister Barbara Castle as her political heroine, and has described her mother and maternal aunt as "two very strong feminists".
Pre-politics, she worked for Amnesty International, Save The Children and the Greater London Authority, among others.
By 2010, she was working with Ed Miliband's successful campaign for the Labour leadership, also spending time as a special adviser to former cabinet minister Tessa Jowell.
She had also been elected to Camden council in north London. After former Oscar-winning actress Glenda Jackson announced she was standing down as an MP, Siddiq was selected as Labour's parliamentary candidate for the Hampstead and Kilburn seat.
Elected to Parliament in the 2015 general election, Siddiq was one of 36 Labour MPs who nominated Jeremy Corbyn for the party leadership, but she backed Andy Burnham in that election.
She would be re-elected in 2017, 2019 and 2024 with much larger majorities.
Appointed a shadow education minister in 2016, she resigned from the front bench three months later to vote against triggering Brexit.
Siddiq is probably best known for campaigning for the release of her constituent, British-Iranian citizen Nazanin Zaghari-Ratcliffe, who was detained in Iran for nearly six years.
In 2017, while campaigning for Ms Zaghari-Ratcliffe's release, Siddiq was asked in a Channel 4 News interview why she had not challenged her aunt, who had been accused of leading an authoritarian government in Bangladesh guilty of human rights abuses.
A row ensued, the programme's editor complained her behaviour to a pregnant producer had been "threatening", and Siddiq apologised.
She married in 2013. Two days before she gave birth to her second child in 2019, she attended the Commons in a wheelchair for an important Brexit vote. Later that month, after a rule change, she became the first MP to vote by proxy.