He served as a municipal councillor and then warden for the Municipality of the District of Barrington.[2] O'Donnell first attempted to enter provincial politics in the 1998 election, but lost to Liberal incumbent Clifford Huskilson by 309 votes.[3] He ran again in 1999,[4] but election night returns had O'Donnell losing to Huskilson by one vote.[5] A judicial recount was held on August 17 resulting in a tie which was broken when the ridings returning officer picked O'Donnell's name from a box.[6][7][8]
A backbench member of John Hamm's government, O'Donnell broke party ranks in June 2001 to vote against Bill 68, the government's anti-strike legislation.[9][10][11] The law ended the right to strike for health-care workers and gave cabinet the power to impose a wage settlement on nurses.[12] O'Donnell voted the way he believed "the majority of people in Shelburne County would want."[13] He was later replaced as head of the Community Services Committee, which the opposition Liberals said was a result of voting against the government.[14][15] On February 17, 2003, O'Donnell announced that he would not reoffer as a Progressive Conservative candidate in the next election, but that he was considering seeking re-election as an independent.[16] On April 8, after re-thinking his decision at the request of Hamm, O'Donnell announced he would re-offer for the Tories after all.[17][18]
In the 2003 election, O'Donnell faced a challenge from former MLA Clifford Huskilson,[19] but was re-elected by almost 600 votes.[20] In the 2006 Progressive Conservative leadership race, O'Donnell was a supporter of Rodney MacDonald, and was named caucus whip shortly after MacDonald took over as premier in February 2006.[21] On May 1, 2006, O'Donnell announced he was leaving politics and would not be running in the 2006 election.[22]
O'Donnell returned to municipal politics in 2008 when he was elected a councillor in the Municipality of Barrington.[23] He was defeated when he ran for re-election in 2012.[24]