[1] He held ministerial office in the governments of Kevin Rudd and Julia Gillard from 2007 to 2013, including as a member of cabinet from 2012 to 2013.

In December 2005, he was elected to the position of Chair of the Federal Labor Industrial Relations Taskforce in a caucus ballot.

The Taskforce investigated the adverse effects of the Howard Government's WorkChoices legislation, a controversial package of industrial relations changes.

On 6 June 2009, O'Connor was announced as the Minister for Home Affairs in the First Rudd ministry, replacing Bob Debus who retired at the 2010 election.

[11] Following Labor's narrow victory, Prime Minister Julia Gillard allocated increased responsibilities to O'Connor.

In this portfolio, O'Connor enacted several key policy reforms including: new and tougher laws to protect children from being procured and groomed online,[12] achieving consensus for an R18+ video game classification after 10 years of debate at Standing Committee of Attorney-General;[13] and introducing significant reforms of the anti-dumping regime in 20 years.

[20] After the ALP's defeat at the 2013 federal election, O'Connor was included in Bill Shorten's shadow cabinet.

He was retained in shadow cabinet when Anthony Albanese succeeded Shorten as opposition leader after the 2019 election.

[21] Following the 2022 federal election, O'Connor was appointed Minister for Skills and Training in the Albanese ministry.