The actual Jack Crichton makes only a brief appearence at first, as he wishes off his son John Crichton in the episode Premiere. It is made clear that the two men are similar in their need to go to space and push the boundaries, but they are doing it in their own very different ways. Where Jack was the hero who went on the early space missions, John is the scientist trying out his first experiment. Despite their differences, Jack is full of support for his son, and wishes him the best as he departs aboard Farscape One.

Jack is not seen for some time then, but his body is. The Ancients, a species capable of wormhole travel, originating from another realm, meet with John Crichton in A Human Reaction to see if Earth would make a suitable home for them. The leader of the group of Ancients comes to John in the form of Jack Crichton. He then retakes this form in Season 3 as he checks up on John's wormhole progress, worried that he has leaked the information into the wrong hands, the Charrids.

The real Jack Crichton makes a reappearence in Season 4 however, when John Crichton manages to find a way back to Earth. At first we see Jack as a younger man, preparing for his first space mission. Something John did altered the timeline, and Jack was scheduled to go aboad the doomed shuttle mission, aboard Challenger. As Jack deals with his family who are against the idea of him going into space this time, John and the rest of the crew aboard Moya work to reshape the timeline, using the "elasticity of time".