[5] Like his former constituency colleague Desmond O'Malley, O'Dea was opposed to Charles Haughey's leadership throughout the 1980s, becoming a member of the so-called Gang of 22.

In January 1992, after Albert Reynolds succeeded Charles Haughey as leader of Fianna Fáil and Taoiseach in coalition with the Progressive Democrats.

In January 1993, in the Fianna Fáil–Labour Party coalition government, O'Dea was reappointed at Justice with the additional appointment as Minister of State at the Department of Health.

After the 1997 general election, Fianna Fáil were back in government in coalition with the Progressive Democrats and O'Dea was appointed a Minister of State at the Department of Education and Science.

He oversaw reform and increased investment in adult education and back to school initiatives, starting with the launch of Green Paper in November 1998.

[8] After a number of changes, including a form of the independent assessment of needs demanded by the disability organisations,[9] O'Dea introduced a new bill in September 2004 along with an implementation package.

[13] He also presided over Ireland's second tour in Lebanon in late 2006, as part of UNIFIL 2[14] and participation in the EUFOR mission to Chad.

In August 2007, he broke ranks with cabinet colleagues to speak out against Aer Lingus's decision to cease London Heathrow Airport flights from Shannon.

However, Green Party Chairman Senator Dan Boyle wrote on Twitter, that he has "no confidence" in O'Dea and declaring him to be "compromised".

[32] O'Dea said he decided to resign when it became clear that the Green Party would no longer support the Government if he was to stay in office.

[33] O'Dea was appointed to Micheál Martin's frontbench as Spokesperson for Communications, as part of the Fianna Fáil campaign for the 2011 general election.

Almost two years after the Coalition Government with Fine Gael and the Green Party was formed, O'Dea remarked that “By now I think you’d have more chance of getting young people interested in the music of Big Tom than getting them into Fianna Fáil,” in reference to the Irish country and traditional music singer.

[35] In 2023, O'Dea voiced his criticism of the decision by the Minister for Justice, Simon Harris, to grant an application by convicted killer Logan Jackson, to move him from Limerick Prison to a jail in the Great Britain, so as to be nearer his family.

O'Dea supported the legal challenge by Tracey Tully, the mother of the murdered champion Irish boxer, Kevin Sheehy.