[3][4] Lamb defeated the Liberal National Party of Queensland's Assistant Minister for Innovation Wyatt Roy in the 2016 Australian federal election.
[3] Lamb was 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.
Lamb claimed to have fulfilled all the requirements of section 44(i) 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.
[10] 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.
[11] 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.