Clarke was born in Phoenix, Arizona. He attended George Washington University in Washington, D.C., where he obtained a bachelor of arts and later a law degree. He joined the FBI as a Special Agent in 1964, working in the Birmingham, Boston, Philadelphia, and Kansas City Divisions as well as at FBI Headquarters. He progressed from Special Agent to Supervisor, Assistant Special Agent in Charge, Special Agent in Charge, Assistant Director, Executive Assistant Director, Deputy Director, and finally Acting Director.
Bill Clinton, the forty-second President of the United States, was inaugurated on January 20, 1993 and resolved to replace then FBI director William Sessions. Sessions was dismissed on July 19 after refusing to resign and Louis Freeh was nominated to the post at a Rose Garden ceremony the following day. Clarke was named acting director, and served from the 19th until September 1, 1993 when Freeh was sworn in.
Clarke then retired from the FBI. He joined McAndrews & Forbes, a private firm specializing in acquisitions, where he is currently Vice President for Corporate Compliance.