After Harley's break up with the Joker, she was deadset on proving herself as a supervillain and get into the Legion of Doom by forming a team of her own. In the episode "So You Need a Crew?" she set out to find members for her team and went to Underworld Talent Inc. to hire henchmen, however, once the consultants discover she is no longer with the Joker, they refuse to give her anything and kick her out. She then went to a seminar on villainy to get some tips from Maxie Zeus but he turned out to only be after sex. After Harley visited the Queen of Fables who told the story of how she was unfairly imprisoned in a U.S. tax code book and telling her of the double standard when it comes to male and female villains, Harley realized she shouldn't try to recruit people who believed in her but rather people no one else believed in. She starts by recruiting Doctor Psycho who has been ostracized and kicked out of the Legion of Doom for his misogyny and calling Wonder Woman and later his own wife a cunt. She also recruits Clayface, who worked as a bartender at Noonan's Bar. As the crew's first mission, they get revenge on Maxie by stealing his gold medals and beating him up.
In "Finding Mr. Right" Clayface recruited King Shark to help Harley find a nemesis, helping them to hack into a website. He also stuck around and helped Harley prove Robin wasn't her nemesis and afterward Harley invited him into her crew, and he accepted because he liked being on a schedule. However, his constant present, caused them to be evicted from Poison Ivy's apartment due to a "no pets" rule.
In "Being Harley Quinn" Ivy's landlord Sy Borgman found the whole crew passed out on the floor and almost cremated them in a pizza oven at Gotham Mall, believing they were dead. Harley looked around the abandoned mall and realized it was the perfect lair for the crew. Sy agreed to let the crew have it on the condition that they would let him come along on some of their heists.
In "New Gotham" Harley gets taken capture by the newly formed Injustice League as they take control of the city. After months, the crew manages to break Harley free and they go on to take down the remainder of the Injustice League.
In "Inner (Para) Demons" Psycho quits the team after Harley set out to take over the city with Darkseid's army of parademons but gave it all up, realizing murdering thousands of people for no reason wasn't what she really wanted. He later betrayed Harley by taking control of the parademons and mind-controlling Clayface, King Shark and later Poison Ivy. He tried to get Ivy to kill Harley to fulfill his deal with Darkseid, in which he promised him to rule the world if he gave him Harley's head. However, Harley managed to break Ivy out of his control and together they captured Psycho who was brought to Arkham Asylum.
- Doctor Psycho (traitor)
- Batman (temporary ally)
- Kite Man
- Queen of Fables (formerly; deceased)
- Mirielle Borgman
- Nora Fries
- Mr. Freeze (deceased)
- Darkseid (briefly)
- Gotham City Police Department
- Injustice League (disbanded)
- Queen of Fables (deceased)
- Scarecrow (deceased)
- Doctor Psycho
- Harley’s crew is known to be her own version of the Legion of Doom, or the Suicide Squad.
- All of them have issues with being accepted in the villain community. Harley is dismissed as Joker's girlfriend, Doctor Psycho is a pariah for his open misogyny, Clayface annoys others with his overly dramatic ways, and King Shark is a skilled hacker, yet most people who hire him only care that he's a Shark Man. The only exception is Ivy, who voluntarily keeps herself isolated from most others despite being asked to join the LOD several times.
- They enjoy doing crime together and form a true bond of friendship that is rare even among the villains of the series.