[4] While attending university, he worked at Woolworths Supermarkets from 1995 to 1998; at MacKillop Catholic College (now St Mary MacKillop College) in 1998 as a cleaner; at the Australian Fisheries Management Authority from 1998 to 1999 as a legal assistant; and at the Commonwealth Department of Transport and Regional Services from 2000 to 2004 as a policy officer, lawyer, and then a senior lawyer.

[5][6] After almost two weeks of deliberations, the Greens chose to support a minority Labor government, thereby consigning Seselja's party to the opposition benches.

[8] He led the Canberra Liberals to their highest-ever number of seats, claiming eight in the seventeen-member ACT Legislative Assembly.

[9] On 23 February 2013, Seselja won his pre-selection bid, and thus became one of the two official Liberal Party Senate candidates for the ACT.

During the 2016 Turnbull government second ministerial reshuffle Seselja was appointed as the Assistant Minister for Social Services and Multicultural Affairs.

In December 2017 as part of a subsequent rearrangement of the Turnbull ministry, Seselja was appointed as the Assistant Minister for Science, Jobs and Innovation.

The mission, supported by both of Australia's major parties and taking place during a "caretaker" period in which Seselja fought for his re-election to the Australian Senate, was considered by observers to reflect strategic anxieties over the deal, which extended to allies New Zealand and the United States.

[23] Seselja abstained from the Senate vote[24] on same-sex marriage in November 2017, despite having promised to honour the national postal result three months earlier.