Michael Clayton (George Clooney) is an in-house "fixer" at one of the largest corporate law firms in New York. At the behest of the firm's co-founder Marty Bach (Sydney Pollack), Clayton, a former prosecutor from a family of cops, takes care of Kenner, Bach & Ledeen's dirtiest work. Clayton cleans up clients' messes, handling anything from hit-and-runs and damaging stories in the press to shoplifting wives and crooked politicians. Though burned out and discontented in his job, Clayton is inextricably tied to the firm.

At the agrochemical company U/North, the career of in-house chief counsel Karen Crowder (Tilda Swinton) rests on the settlement of the suit that Kenner, Bach & Ledeen is leading to a seemingly successful conclusion. When the firm's top litigator, the brilliant Arthur Edens (Tom Wilkinson), has an apparent breakdown and tries to sabotage the entire case, Marty Bach sends Michael Clayton to tackle this unprecedented disaster and, in doing so, Clayton comes face to face with the reality of who he has become.