[1] Thistlethwaite is a senior figure in the Labor Right faction and stands as the current convenor of the NSW branch.

[2] Before joining Parliament, he was the general secretary of the New South Wales branch of the Australian Labor Party.

[3][1] In this role he represented workers in public sector enterprise agreement negotiations and in the NSW Industrial Relations Commission.

He was a co-ordinator of the Your Rights at Work campaign in New South Wales against the Howard Government's WorkChoices laws.

[citation needed] Before entering Parliament, Thistlethwaite worked as a senior consultant with law firm Mallesons Stephen Jaques.

[3][1] Thistlethwaite sought to become the endorsed Labor candidate for the House of Representatives seat of Kingsford Smith in Sydney's eastern suburbs, for the 2004 election.

[9][10] Following the announcement by Peter Garrett that he would not recontest the seat of Kingsford Smith at the next federal election, Thistlethwaite announced on 2 July 2013 that he would again seek Labor preselection;[11] and gained endorsement on 20 July 2013, defeating Tony Bowen, the mayor of Randwick and son of former Kingsford Smith MP Lionel Bowen.

The Australian reported that "by becoming the NSW factional boss, Thistlethwaite de facto takes the title of national Right convener".

A freedom of information request revealed that as of October 2023, only two documents had been produced and one meeting held in relation to Thistlethwaite's portfolio as Assistant Minister for the Republic.

[16] On 29 July 2024, as part of the Albanese Government's first ministry reshuffle,[17] Thistlethwaite was made Assistant Minister for Immigration.

[5] Thistlethwaite lives in Matraville with his wife Rachel, a nurse,[5] and their four daughters Amelie, Scarlett, and twins Eliza and Camilla.