At the New York law firm of Kenner, Bach & Ledeen, Michael Clayton (GEORGE CLOONEY) is the go to guy when things need fixing in ways that can't be handled in the courtroom or via traditional legal methods. Although the former prosecutor is quite good at what he does, he isn't happy, which is why he's recently tried to open his own restaurant. Yet, thanks to bad dealings with his alcoholic business partner brother, Michael's $75,000 in debt, and his former gambling addiction isn't helping matters.
Nevertheless, he must still do his job, and his latest assignment is finding his former mentor, Arthur Edens (TOM WILKINSON), the firm's chief litigator in a multi-year and multi-billion dollar class action lawsuit representing the agrochemical company U/North.
A manic-depressive, he's apparently gone off his medication and had a breakdown during a deposition, stripping down to just his socks in the courtroom before disappearing from sight. U/North's head honcho, Don Jefferies (KEN HOWARD), wants his company's lead counsel, Karen Crowder (TILDA SWINTON), to resolve matters quickly, a point shared by the law firm's two bosses, Marty Bach (SYDNEY POLLACK) and Barry Grissom (MICHAEL O'KEEFE).
Wanting to help his friend before he does any more damage to his career or their law firm, Michael sets out to find him. Yet, as he starts his search, various discoveries and revelations begin to cloud his judgment, leaving him in a quandary about what to do. With Karen driven to desperate measures to try to prevent any potentially damaging information about U/North from being released, Michael must decide whether to do what's right or what's best for him.