Judge Duffy-Lewis began her legal career in a diverse private practice ranging from airline deregulation and aviation law to family law.   She later joined the L.A.D.A. and prosecuted major felonies.   While at the DA's office, she prosecuted the case of People v. Daniel Jenkins.  During the prosecution of this case, her investigating officer, Detective Thomas C. Williams of the LAPD, was executed by Jenkins (out on bail) in front of the elementary school his child attended, on Halloween Day, 1985. This case was responsible for changing the California bail laws.  Daniel Jenkins is now on death row awaiting execution.

A native Angeleno and Eagle Rock high school graduate, Judge Duffy-Lewis earned her undergraduate degree at the University of Southern California and her juris doctorate degree from Loyola University School of Law in Los Angeles.  She was appointed to the Municipal Court bench in 1987 by then-governor George Deukemjian and was elected to the Superior Court bench in January 1996.  Since 2003, Judge Duffy-Lewis has been assigned to Dept. 38, Unlimited Jurisdiction, Fast Track, Stanley Mosk Civil Courthouse in Los Angeles.