[1] In 2018 O'Byrne was re-elected to the House of Assembly with a strong personal vote topping the Labor ticket.

[3] An independent investigation conducted by Barbara Deegan, a former commissioner of the Commonwealth industrial tribunals from 1996 to 2014, found that his actions were "inappropriate" and “wrong” but did not constitute sexual harassment.

He has fought for job security for public school cleaners and grounds people, as well as for greater recognition for early years professionals.

While with the LHMU, O'Byrne led the Union's campaign to make Tasmania the first state to protect hospitality workers and the public by introducing a ban on smoking in enclosed areas of bars and casinos.

O'Byrne has made significant contributions to the community through his roles as chair of Smoke Free Tasmania, member of the Ministerial Advisory Council on Child Care, member of the State Facilitating Group Anti-Poverty Week Organising Committee, co-chair of the Anti-Poverty Week Organising Committee, founding member and chair of the Peace Coalition (a group established to protest the invasion of Iraq), and treasurer of the Tasmanian Peace Trust.

O'Byrne was preselected as an endorsed Labor candidate for the Tasmanian House of Assembly electorate of Franklin on 21 July 2009.

O'Byrne's ministerial responsibilities originally encompassed Environment, Parks and Heritage; Workplace Relations; Arts; Sport and Recreation and the newly created Hospitality portfolio.

O'Byrne held the portfolios of Economic Development, Infrastructure, Workplace Relations, Innovation, Science and Technology, and Police and Emergency Management.

[13] Citing a need for the Parliament to be stable in the minority government situation that emerged after the 2024 State Election, O'Byrne agreed to provide limited supply and confidence to Premier Jeremy Rockliff by committing to passing the government's budget bills and agreeing to not support frivolous no confidence motions.

O’Byrne publicly admitted to sending sexually explicit texts and kissing a young staff member.

Much media attention ensued as former Labor Premiers Lara Giddings and Paul Lennon called publicly for his resignation from Parliament.

[17] However, in 2023, O'Byrne announced he would seek Labor preselection for Franklin at the next election, despite White letting it be known that he would be not welcome in caucus as long as she led the party.