Jackson was a Maquis fighter who served on the raider the Val Jean under Chakotay until 2371.
In 2371 the Val Jean and the USS Voyager were both stranded in the Delta Quadrant by the Caretaker's array. The Val Jean was destroyed when it was rammed into a Kazon warship while fighting the Kazon-Ogla. As a result, the crew of the Val Jean, Jackson included, joined the crew of Voyager as Starfleet personnel on its historic trek home from the Delta Quadrant. (VOY: "Caretaker")
Jackson was involved in a 'Maquis operation' with Seska in order to steal mushrooms from Neelix to make mushroom soup for Chakotay. Due to this, Jackson's replicator privileges were revoked for two days. (VOY: "State of Flux")