Making his debut in the Season 1 episode "The Scene," Walsh is first hired by Vince to direct his upcoming movie, Queens Boulevard, on account of his triumph at the Sundance Film Festival with his indie movie Daze. He partially rewrites the script to include a scene in which Vince's character has a homosexual encounter. The boys worry over the scene, but Walsh persuades Vince of its viability as a test of his commitment to the project - by admitting that the scene will not be made at all. The team shoots the movie in New York during the interlude between Seasons 1 and 2.
In season 2, Walsh aims for a second Sundance trophy by successfully submitting Queens Boulevard for exhibition, but defiantly insists that James Cameron - whom Vince wants to meet to firmly land the title role in Aquaman - watch it at the festival instead of sending him a print. The movie is eventually well received. In the third season, the studio prepares to release QB for a wider audience, but Walsh seeks an injunction because the general-release version would be colorized; it is implied that he was denied the injunction. Late in the season, the gang brings back Walsh - who is working as a porn film director - to direct the shooting of Medellin after he reads the script, knowing his ability to make quality films with small budgets. He agrees on the condition that he will have final cut. He later decides it will be shot in Spanish.
In the fourth season, the gang goes down to Colombia to shoot Medellin. However, Walsh falls apart on the set over the course of the shoot, with some of his antics include banning cellphones during production meetings, violently firing a director of photography for poorly shooting a scene, conducting witch hunts to see who may have seduced a local woman hired for the shoot, and tapping Stephen Gaghan to help him rewrite the ending when he already revised it. Billy finishes filming the final scene of the movie, a military assault scene that he is pleased with. Walsh's conflicts in Colombia with E, whom he derisively calls "suit," continue in Los Angeles for most of the season. Per his final cut authority, he avoids Vince and E from showing them the first cut and also refuses to consider editing it further after they see it. The Cannes Film Festival committee also accepts Medellin for screening, but not before Walsh gets angry at E for supposedly leaking the copy of a trailer (it is revealed that an editor's girlfriend did). Walsh hires Ari as his agent after Ari signs him, Vince and E to do a new movie, Lost in the Clouds. Knowing E's pledge to never work with Walsh again, Vince tries to get Walsh off the movie. Walsh fires Ari over a threat about being sued for breach of contract because he disposed the Lost in the Clouds script to make an entirely new script for a sci-fi film called Silo. Upon learning that Anna Faris is being managed by E, Walsh tries to get her aboard for the film, but she does not understand the script. He joins the gang in flying to Cannes for the Medellin premiere in the season finale "The Cannes Kids" but as with Cameron in Queens Boulevard, he refuses to let Yair Marx see the film. E's warnings about a failure to edit the film come back to haunt him as the audience jeers away at Medellin after the world premiere. It is implied that this failure has resulted in the cancellation of the Silo project and it effectively ends Walsh's movie career.
Billy returns in the season 7 episode "Hair" looking to find work again to feed his family. He explains that he had spent the past two years reforming his ways - including being an ordained minister - and specifically approaches E for help. Over the rest of the season, Billy works with Drama to create a new animated series called Johnny's Bananas. In the final season, Walsh is temporarily rankled that Drama and Andrew Dice Clay's labor strike could cost him his job. He also steps in to fix Vince's miner movie script and to direct it as well. The final fate of the project is left unknown with the ending of the series.
Billy appears in the Entourage film. in which he is shown, with other celebrities and guests following a party, awaiting to see Vince's directorial debut project Hyde.
He also appears in a mid-credits scene, in which Ari's former assistant Lloyd has his wedding and Ari gives him away. When the group gets together for a picture, Billy Walsh suggests that they should make a film (or TV show) about the lives of Vince and the gang.
Personality and traits Edit
Billy has a mercurial, intimidating personality, which comes from his early success as the youngest director ever to win the Sundance Film Festival. He also claims to paint. According to interviews on the season 2 DVD, Billy is mainly inspired by Entourage writer Rob Weiss and Vincent Gallo and secondly another indie director Quentin Tarantino. Billy is from a wealthy family having grown up in New York suburb of Scarsdale and his exposure to Queens is limited to a supermarket his father owned there. (Weiss is from the wealthy, predominantly Jewish Five Towns area of Long Island). While he thinks of himself as an artist and shows scorn for the studio system (He yells "Fuck commerce!" at a press meeting for Queens Boulevard), he also hoped to sell Medellin to a studio that could win him an Oscar. However at Cannes Medellin flopped; when the credits roll he goes on to insult French people in the audience, though for the somewhat noble cause of demanding respect for the crew of the movie. By season 7, Billy has noticeably changed his ways and is redeemed; now not being hostile or egotistic, with respect, making peace with E, successfully trying to find some work to support his family and also attempting to dissuade Vince from his drug and alcohol abuse road in season 7, which Billy had taken before.