James "Jimmy" Lishman, also known as Steve Wilton and Jack, is a handsome, well-bred guy with a lot of moxie. He is pursuing Fiona hard, and he is not afraid to punch out and moon a notorious bouncer to defend her honor. He drives a sports car, wears an expensive watch and throws money around liberally, which Fiona finds off-putting. But he might not be all that he seems...
The problem with Jimmy is not that the things he did were shameless, but that they were often in service of his own needs and desires. It was very rare that he ever did anything that was solely for the benefit of someone else.
During Season 2, Jimmy returns. He marries a Brazilian woman named Estefania, as a way for her to come to the USA. He and Fiona go on a double date, during the date they excuse themselves for a moment and catch up in the bathroom with Jimmy attempting to admit his love for Fiona. At a party thrown for Karen, Jimmy tries to apologize to Fiona for what happened in the bathroom but she insists nothing happened. It is later revealed that a spurned Jimmy had sex with Estefania.
During Season 3, Fiona begins to see more of Jimmy's personality and mentions to Kevin and Veronica that he cleans the house and babysits Liam like he is the father of the house. One day, a black vehicle shows up parked on the street while Jimmy is babysitting Liam. He notices the black car outside the window and tries ignore it at first but is tempted to walk outside and then towards it to see what is happening. It drives off in a hurry and a few more black cars drive off as well, but the first car makes a U-Turn and while Jimmy tries to make a run for it he gets cornered and Estefania's father steps out and holds a gun to Jimmy's head while asking for the location of his daughter. They take Jimmy, leaving the front door of the Gallagher house unlocked and Liam inside. After school ends Carl and Debbie come home to find Liam alone watching TV. Jimmy is kidnapped and taken to Estefania who is surprised to see her father. Estefania greets her father but Marco walks in naked wearing glasses and earplugs. Estefania yells for her father to stop but he shoots Marco in the forehead.
Afterwards, Jimmy is enlisted in helping chop up the body. He refuses but is obligated by the drug lord himself. He returns home and is caught burning his clothes by Fiona. The next day, Jimmy is taken to the Great Lakes on a yacht. The drug lord's henchmen throw Marco's remains into the lake and afterward the drug lord explains that he knows he has been lied to. He goes on to tell Jimmy that he came from a poor background and has always wanted what's best for his daughter. He explains that he has arranged for Estefania to study Economics and in 5 years she will become a US citizen provided that Jimmy is her husband when that time comes. He goes on to tell him that he can have sex with Fiona for fun and only fun since he is married, calling Fiona a "ghetto whore". Jimmy agrees out of fear for his life and returns to his life with a new problem.
As of May I Trim Your Hedges?, he knows of his dad's sexual orientation. Since then he has been consistently talking about his dad and Fiona eventually tries to tell him to stop, but does not do it since the city wants to work on some pipes in the backyard where Ginger was set to be buried. Jimmy begins to realize past signs of his father's sexual orientation from his childhood memories. Jimmy and Fiona had an argument, and he left out of anger. He goes to Estefania and explains his problem. The two have had sex more the once. Fiona calls Jimmy when the day is finished, and apologizes to him.
His relationship with Fiona is slightly halted when he decides to go back to medical school in Michigan. He asks Fiona if she wants to go and and if the kids would go with them. Fiona is shocked, but happy for him. When an application was accepted for a studio apartment in Michigan, Fiona gets upset. Fiona confronts him outside the work site and Jimmy says that he has been living in a slum with Fiona and the kids, as well as saying that they have never made decisions together. Fiona storms away in anger.
Estefania's father shows up the next day and tells Jimmy that his daughter is being deported for failing to impress the INS, who had been watching Jimmy and Estefania. Jimmy is then taken on Estafania's father's boat and Jimmy is refused a final call to Fiona. It is assumed, though uncertain, that Jimmy met his death at the hands of Estefania's father.
Jimmy has since disappeared, and Fiona starts to worry. She attemps to call again a few times, and went to look for his dad, Dr. Ned Lishman, but eventually, the guy who followed Jimmy gives Fiona an envelope of money, supposedly from Jimmy. The guy explains that Fiona is too good for him, but when Fiona tries to find out more, he drives off. Later, Fiona calls Jimmy and leaves him a final message: goodbye. He has only been mentioned scarcely since.
At the ending of Lazarus it is revealed that Jimmy is alive, and is with an unknown woman. Taking up the alias "Jack", he and his female accomplice pull up to the Gallagher house and she asks him if this is the house, and if he wants to go in. Jimmy says "No, not tonight."
Jimmy makes an appearance in Rite of Passage. After greeting her mysterious female customer, now known as Angela, "Hey, you came back after all!", Fiona is answered by Jimmy from across the restaurant booth, who states "I did."
During Tell Me You F**king Need Me, Fiona tells her husband, Gus, that she cheated on him and Gus wishes to meet Jimmy. Jimmy agrees and they meet at Patsy's Pies. Jimmy says hello to Gus then Gus punches him in the nose and walks off. Soon after, Jimmy comes and sits outside with Fiona where she explains she doesn't want to be with Jimmy because she needs something different and doesn't live for Jimmy's dangerous personality any more. Jimmy then follows the footsteps of Gus and walks off. Jimmy musters up courage and tells Fiona to have a good life, and she says the same. Jimmy drives off on his motorcycle and Fiona starts walking off. Angela shows up in her expensive car and says she likes Fiona and calls 'Jack' an asshole.