At the end of season 3, Ian, still underage, enlists in the Army using his brother Lip’s identity.
In season 4, it is revealed that he has deserted training camp, stolen an army helicopter, and is being pursued by Army for possible charges.
When season 4 begins, he is working as a dancer and a rent boy at a gay bar called The White Swallow while squatting in an abandoned house. Lip and Debbie track him down and try to persuade him to return home.
However, when Mickey Milkovich finds Ian at the club passed out on drugs he carries him back to his house.
Ian’s behavior becomes more and more erratic and he is diagnosed with Bipolar disorder, which also affected Monica. Ian is offered treatment but refuses it despite his family’s encouragement. In season 5, episode 10, Ian is arrested then released soon afterwards into Monica’s care. When Monica takes Ian to live in her trailer, he discovers she is using methamphetamine and he leaves.
He returns to the Gallagher household and by the end of the season has ended his relationship with Mickey, citing his mental illness. In season 6, Ian visits Mickey in prison. Mickey asks Ian if he’ll wait for him but it’s quite obvious that Ian is over him. After being tired of getting bossed around by Fiona, Ian quits his job at Patsy’s Pies, and Lip gets him a job as a janitor at the college. Ian thinks Lip and his friends are making fun of him and they get into a fight. When Ian sees a car crash occur, he rescues a woman from a burning car. He passes out and is saved by a firefighter.
Ian eventually meets a firefighter named Caleb (Jeff Pierre) with a religious priest father who disapproves of his homosexual lifestyle. Caleb convinces Ian to lie about his bipolar disorder when he applies to be a paramedic. Ian does get fired but convinces them to let him keep his job. Ian later discovers that Caleb has been cheating on him with his female friend from high school and they break up. Ian then meets a trans man named Trevor and they begin dating.
Ian soon finds out that Mickey has escaped from prison and “kidnaps” Ian and asks him to go to Mexico with him in season 7 episode 10 and Ian decides to go with him. However at the Mexican border, Ian realizes that he has changed and decides not to go, devastating Mickey. Ian tells Mickey he loves him for the first time. He and Mickey kiss, say goodbye and Mickey sneaks into Mexico. After this, Ian apologizes to Trevor and they break up.