He has been a Member of the Northern Ireland Assembly for Upper Bann since 2003, and has served as Minister for Finance since February 2025.

He briefly took on the duties of deputy First Minister in 2011 while Martin McGuinness ran in the 2011 Irish presidential election.

[6] In 2003 he was elected as MLA for Upper Bann and in 2005 unsuccessfully contested the same-named Westminster constituency.

[4] On the 13 May 2022, he was confirmed as the 'caretaker' Infrastructure Minister replacing Nichola Mallon of the SDLP who failed to retain her seat in the previous week's election.

[7] After Sinn Féin nominated Martin McGuinness as its candidate in the 2011 Irish presidential election, O'Dowd took over the duties of deputy First Minister on a temporary basis from 20 September to 31 October 2011.