O'Donnell was a Maquis fighter who served on the Maquis raider Val Jean under Chakotay until 2371 when he joined the crew of the USS Voyager after the Val Jean was stranded and destroyed in the Delta Quadrant. (VOY: "Caretaker")
A hologram of O'Donnell helped Chakotay take the ship in Tuvok's holodeck program entitled Insurrection Alpha. In the scenario, he and Carlson were on the bridge when Chakotay commandeered Voyager. They later escorted the prisoners who refused to join under Chakotay's leadership to the brig, where he remained to guard the imprisoned bridge crew.
O'Donnell was part of the security away team which accompanied Captain Janeway and Seven of Nine aboard the USS Dauntless, where he tried to stop Arturis when he activated the quantum slipstream drive. He was unable to stop him and beamed aboard the Voyager. (VOY: "Hope and Fear")