O'Neil joined the Australian Labor Party at 16 and soon met Simon Crean, former party leader and her predecessor as the member for the division of Hotham. In her maiden speech, O'Neil described Crean as one of her "Labor heroes" and "a person in whose footsteps I am honoured to walk". In March 2003, O'Neil ran as a candidate for Springvale South Ward in the City of Greater Dandenong and was subsequently elected. After one year in the position, she was also elected as mayor, becoming the youngest female mayor of a local government area in Australian history. 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. In 2009 O'Neil began work for the global Management consulting firm McKinsey & Company. O'Neil was endorsed as a late replacement candidate for the Australian Labor Party in Hotham at the 2013 Australian federal election, following the disendorsement of her friend Geoff Lake. She retained the seat for Labor and was quickly flagged by political commentators as a future Labor front bencher.
In Parliament
From 2013 to 2016, O'Neil served on the House of Representatives standing committees on Agriculture and Industry and Tax and Revenue. Following the 2016 election, O'Neil was appointed to the shadow ministry under opposition leaderBill Shorten, becoming Shadow Minister for Justice. She was additionally made Shadow Minister for Financial Services in June 2018. 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.
In her maiden speech O'Neil placed an emphasis on the importance of a strong economy in effecting a fair society and stemming disadvantage. She stated that whilst she believed "government should not be building great tariff walls or controlling the big macroeconomic levers", it did in practice provide "the platform on which our businesses compete – and win – globally" and that political leaders must therefore play a role in providing "good policy and clear communication" on the topic. 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.
Indigenous Australians
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. I want my generation to be the last to have to say it."
Political Inspiration
When asked to nominate those political figures she most admires, O'Neil has said that she draws inspiration from Julia Gillard, an "absolute political warrior"; Tanya Plibersek, the former deputy opposition leader; and Jenny Macklin. O'Neil said she admired their ability to "maintain a good sense of what it is to be a woman but also survive in a very masculine and antagonistic political environment" and that she would be observing Plibersek and Macklin in Parliament "to see how it's done".
EMILY's List
O'Neil is a member of EMILY's List Australia, a political network with ties to the Australian Labor Party that supports progressive female candidates for election to public office.
O'Neil lives with her partner Brendan, an anaesthetist, and their young son. While living in the Northern Territory, O'Neil and her partner also cared for a child as foster parents. She does not live in her electorate but in the nearby Division of Melbourne.
