[3] In 2006, she was awarded a Fulbright Scholarship to undertake a Master of Public Policy at Harvard University's John F. Kennedy School of Government.

[7][8] In 2007, while studying in the United States, O'Neil worked as an intern on the New York Stock Exchange; and in 2008 returned to Australia to serve briefly as an adviser to the Office of the Commonwealth Treasurer.

[9] She retained the seat for Labor and was quickly flagged by political commentator Peter van Onselen as a future front bencher.

[3] After Labor lost the 2019 election, O'Neil considered standing for the deputy leadership of the party, but subsequently announced that she did not have enough support from her colleagues and would not contest the position.

[12] ABC News reported that she was persuaded to drop out in order to make way for fellow Victorian Right MP Richard Marles.

[18] On 2 September 2022, she announced a comprehensive review of Australia's migration system to address existing challenges and set a new direction for the coming decades.

[26] She has also spoken on issues such as human rights violations in Cambodia,[27] primary, secondary, and higher education,[28][29] asylum seeker policy,[30] and Australian Labor Party reform.

O'Neil cites her family's history, work at McKinsey & Company, and experiences in indigenous communities as influential in shaping her views on the economy.

'[32] In 2011, O'Neil spent nine months living with her partner in North East Arnhem Land, one of the northernmost regions of the Northern Territory, fostering a child and assisting local women to establish small businesses.

During her time in the region, she witnessed crises in health, housing, and employment; and she has since spoken in Parliament on her desire to see action taken to resolve them: "For many decades politicians have said it is shameful.