Born in Mackay, Queensland, Lamb was a teacher aide, then a lead organiser with United Voice from 2012. Lamb defeated the Liberal National Party of Queensland's Assistant Minister for Innovation Wyatt Roy in the 2016 Australian federal election. The LNP had expected to retain the seat located in Brisbane's northern suburbs only to lose by a small margin of 0.79 points. Lamb is implicated in the 2017–18 Australian parliamentary eligibility crisis as she was alleged to be a British citizen by descent through her deceased father, who was born in Scotland. She had attempted to renounce her British citizenship before nominating for election in 2016. However, her renunciation form was refused by UK authorities as they were not satisfied that she was in fact a British citizen, and requested further documents as evidence. Lamb claimed to have fulfilled all the requirements of section 44 as she believed she had taken all reasonable steps to renounce her citizenship – if it were the case that she was a British citizen – as she was unable to provide any further documents; she said she was "estranged" from her mother and that her father had died. On 7 February 2018, she gave a longer description of her life story in a speech to the House of Representatives. The British government requested her British passport and her parents' marriage certificate. She claims her mother left the family when she was six years old and she has no relationship with her mother as her father had died. However, Lamb's mother and stepmother later contradicted her version of the story. It was revealed that she and her mother had maintained contact at least until 2014 and her mother helped organise her wedding. The government stated that it believed that her situation should be referred to the High Court for a decision on her eligibility. On 9 May 2018, Lamb announced her resignation from the House of Representatives following the High Court of Australia ruling that Senator Katy Gallagher was ineligible to contest the 2016 election. On 15 May, the Labor Party released documentation from the UK Home Office confirming that Lamb's citizenship had been renounced the previous day, clearing her to nominate as a candidate for the Longman by-election. She was re-elected at the by-election held on 28 July.
