Born August 31, 1953 in Berkeley, California to Roslyn Mazer and Abraham I. Klecks, an executive for the FDA. Attending UCLA from which she graduated in 1974 with a BA, Clark went on the Southwestern University School of Law, graduating in 1979.

After a couple of years with a private law firm, Clark joined the Los Angeles DA's office in 1981. Among the cases she prosecuted was that of Albert Lewis and Anthony Oliver, sentenced to death for the 1989 shotgun murders of two people who were gunned down praying inside a church. Her highest profile case became the prosecution Robert Bardo, who stalked and killed actress Rebecca Schaeffer.

Her most famous case was as lead prosecutor in the O.J. Simpson murder trial. Simpson was accused of murdering ex-wife Nicole Simpson and her boyfriend Ron Goldman June 12, 1994. The trial took place in an un-precedented media feeding frenzy which quickly catapulted Clark to national fame. The trial, which lasted more than a year, ultimately ended with Simpson being found not guilty of all charges.

During the trial, Clark made a notable change in her public image, her dress and hairstyle. She became "softer," more feminine in response to criticism that her appearance made her seem cold and castrating. Media consultants told Clark that the mock jurors found her offensive, a tough woman lawyer, and that the case would be better served if she became more "womanly," with a face-framing hairstyle, more pastel-colored clothing, and talk of her children and woman's problems.

Clark had a well-publicized child custody battle in the midst of the OJ trial, ultimately re-gaining custody of her children. She gained further publicity in the wake of the trial as a speaker, and published WITHOUT A DOUBT, her reminiscences of the trial, in 1997.