Throughout the Seasons
We meet Steve (Jimmy) in the Pilot Season 1. He's watching Fiona dance at a club and sees her purse get stolen. He chases after the robber unsuccessfully, but he meets Fiona and there is an instant spark. Initially, Fiona thinks that Steve is a hotshot businessman who makes a ton of money. While he does make a lot of money, he proves to Fiona that he isn't her typical snobby rich guy. He makes a living by stealing cars - and he's pretty good at it. Fiona is attracted to Steve's rebel persona.
Steve once got Frank sent to Canada in Frank the Plank, though is forced to help in smuggling him back after being scolded by Fiona.
It is revealed in It's Time to Kill the Turtle, that what Fiona doesn't know is that Steve's real name is Jimmy and that he grew up in Chicago in a very rich household. His brother and the rest of Jimmy's family thinks he is away at medical school, when in fact he is still living in Chicago and making an illegal living. He comes to the Gallaghers' house and spots Frank now drunk sitting in his chair. Steve/Jimmy goes to bond with Fiona.
During But at Last Came a Knock, he continues to see Fiona with whom Jimmy has a heated relationship with and is always at the Gallagher house. When Debbie becomes suspicious, she secretly visits his parents' house and learns his true identity, to his worry.
In Nana Gallagher Had an Affair, he buys the house next door so that he and Fiona can move in together but still stay close to the family. He faces a new problem with Debbie now aware of his true name and threatens him if he hurts her sister. At one point, Tony stops him and congratulates him on being with Fiona and wishes him luck. At the family dinner, Jimmy is present when the Gallaghers dine and is amused by the drama that takes place such as Ian being the half-brother and cousin of his family from Monica's affair with Frank's brother, the argument of Frank, Monica, and Bob, and Frank kissing Monica. The Gallagher’s later stay at Steve’s house where they watch Bob and Monica pack up unsure if they are going to take Liam. They then see Bob, Monica, and Liam come outside. He watches Monica tearfully gives Liam to Fiona, showing that she can’t separate him from his siblings.
In Daddyz Girl, Tony discovers that Jimmy is stealing cars and after beating him up threatens to turn him into the police unless Jimmy agrees to leave the country and leave Fiona behind. Jimmy bribes Tony by giving him the house he bought for him and Fiona and he leaves the country, hoping that Fiona will follow him. In the end, Fiona decides to stay in Chicago and she and Jimmy break up. Jimmy runs off to South America.
In Can I Have a Mother, Jimmy returns and has married a Brazilian woman named Estefania, as a way for her to come to the USA. He meets with Fiona and they talk and he learns of her recently released grandmother before offering for Fiona to 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. In the bathroom he and Fiona start making out, only for Fiona to reject him and leave the bathroom. When she left, Jimmy following short after, Fiona's boyfriend at the time picks up what's going on and leaves her. At a party thrown for Karen, Jimmy tries to apologize to Fiona for what happened in the bathroom but she insists nothing happened. He is shocked to witness Fiona's grandmother Peggy pull a gun and stops her from shooting at Shelia. He panics at the chaos done to everyone. Very soon, Debbie informs Fiona of his real name and she leaves him an angry voicemail while calling his real name. It is later revealed in A Bottle of Jean Nate, that a spurned Jimmy had sex with Estefania. Him and Estefania continue to be 'married' while he is trying to obtain Fiona's heart once more. However, she rebuffs and confronts him on lying to her about his real name and tells him to leave. When Fiona's friend Jasmine invites her onto a boat she finds out that Jasmine also invited Steve and Estefania, in an attempt to get Jimmy and Fiona back together. When they meet, Fiona is more calm and asks Jimmy if he was going to tell her about his real identity. Jimmy admits that he was planning to but never got the chance and Estefania calls for him, causing him to leave while Fiona just gets more pissed at Jimmy, before leaving the boat.
Throughout the rest of season he is shown going to the Gallagher household bringing Starbucks and Dunkin' Donuts to the kids even through Fiona's consistent refusal of him not coming to her house. When Lip runs away from home because of not wanting to go to school, Jimmy lets him stay at his house since Lip says that Fiona will be on his doorstep in a few days if he did so. Lip also helps Jimmy with some computer business to get money and starts doing business with him.
In the last two episodes Jimmy keeps trying his plan to win back Fiona's heart and trust and finally succeeds on the second to last episode after kissing her. On the last episode Jimmy makes it official and they begin dating again.
Fiona begins to see more of Jimmy's real 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 threatened 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 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 Estefania's father's boat and Jimmy is refused a final call to Fiona. In perhaps the show's most shameless moment, 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 attempts 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: Wherever you are, bye.
After being absent for the whole season, He makes an appearance in the finale, Lazarus. After the ending credits, it is revealed that Jimmy is alive, and is with an unknown woman. Taking up the alias "Jack", he and the unknown woman pull up to the Gallagher household 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."
At the beginning of "Crazy Love," Fiona punches and kicks Jimmy and yells at him. Fiona soon stops and tells Jimmy that she moved on by getting married. That night, he visits the Gallagher House, where he meets Fiona and her family. He is told of things that occurred in his absence; such as Fiona's new half-sister and nephew, Liam's near death experience and Fiona's arrest because of it, and Ian's recent action. Fiona soon cries while he comforts her before she stops crying and kisses Jimmy. He spent the night afterwards and was hidden by Sammi to prevent Fiona's husband from seeing him. Later on, the next night comes and Fiona starts to have regrets on their affair. It was here where Jimmy confesses his love to Fiona, before they have sex on the kitchen floor but Fiona stops it before he is finished and has him leave her house.
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 and tells her he called off an overseas job to stay with her. She explains she can't see Jimmy any more and he musters up courage and tells Fiona to have a good life, and she says the same, whatever your name is. Jimmy drives off on his motorcycle and Fiona starts walking off. Angela shows up in her car. Fiona tells her sorry Jimmy canceled the overseas job. Angela reveals the client, not Jimmy canceled, that she likes Fiona and says 'Jack' is a great thief but a shitty person.