Faith came from a broken home with an alcoholic mother, Faith became a slayer when Kendra was killed. Having fought and lost to Kakistos and watch him kill her watcher, Faith runs to Sunnydale to find the all famous Buffy. Although she tries to fit in with Buffy and her friends, Faith cannot get away from the pain in her short life and is a totally different kind of person and slayer to Buffy. Things go further wrong when her new watcher turns out to be a fake, and the real one turns out to be a wuss. Still desperate for some kind of connection to the world, Faith makes out with Xander and takes his virginity, but their passion is very short lived. The final straw for Faith comes when she mistakenly kills the Deputy Mayor, although Buffy tries to reach out to her, Faith shrugs off what she has done and even tries to put the blame on Buffy.
Angel, however, is the one person who knows where Faith is at, capturing her he almost gets through to her when Wesley and the watcher's council intervene and take the slayer captive themselves. She makes short work of them and finally finds someone she can trust and a father figure in The Mayor. Going to the dark side certainly suits Faith and she falls right into place, thinking nothing of betraying her old friends and doing the Mayor's dirty work. This includes trying to seduce Angel in order to turn him back into Angelus and, when that doesn't work, shooting him with a poisoned arrow, the only antidote to which is the blood of a slayer. This last act proves to be her biggest mistake, when Buffy comes after her and the ensuing fight leaves Faith with an almost fatal stab wound and in a coma for eight months.
When she awakes she finds things a lot different. The only person that she believes ever really cared for her is dead, however, he has left her a gift, a device which will enable her to switch bodies with Buffy. Having done so, she ensures that Buffy (in her old body) is safely out of the way and then gets on with Buffy's life. Living in Buffy's body she finds that the world is a different place, one where people feel genuine affection for her and where she is able to do good. Of course, Buffy manages to escape and find a way to reverse the switch. Beaten and confused, Faith leaves for LA.
Here she finds herself tracked down by evil law firm Wolfram & Hart, who hearing there is a slayer in town, think this is just the way to get rid of Angel. Faith accepts the job immediately and sets about luring Angel into a fight by kidnapping and torturing Wesley. She gets her fight but it soon turns into a death wish on her part when she begs Angel to kill her, when instead he just holds her. Despite what she has done, Angel offers her sanctuary and the chance to start her life over, but Buffy, watcher's council and the police, have other plans for Faith. Wanting redemption and realising it is the only thing she can do, Faith hands herself into the police.
Faith serves her sentence diligently, trying her best to keep out of trouble and pay for her crimes, Angel loses his soul again and Wesley busts her out of prison, knowing that she is the only person that can save Angel. Knowing that Angel is the only person ever to have had true faith in her, she sets about saving him, even going to the lengths of taking a lethal dose of the drug Orpheus in order to drug Angelus when he bites her. Back in a comatose state and while Willow makes the trip to Los Angeles to help restore Angel's soul, Faith and Angelus share an hallucination where he takes her through his life as Angel and finally the good wins over the bad and Faith wakes up just in time to save Angel from Connor.
With her duty done by Angel, Faith agrees to return to Sunnydale with Willow and help in the battle against the First. Back in Sunnydale, she finally makes it up with Buffy and the rest of the gang, and despite a few hiccups, and a liaison with the new Principal, Faith plays her part in Sunnydale's final battle and makes it through to the end.