She then worked as an Assistant United States Attorney in Chicago for nine years, trying major felony cases and appearing before the Seventh Circuit.

An Independent, President Ronald Reagan nominated her on March 13, 1985, to a newly created seat on the court, and she was confirmed by the Senate on April 3, 1985.

Her confirmation made her the first woman judge of color appointed to serve on a district court in the three-state Seventh Circuit.

[2] Still an Independent, on August 5, 1999, President Bill Clinton nominated Williams to fill a vacancy on the United States Court of Appeals for the Seventh Circuit caused by the death of Judge Walter J. Cummings Jr..[4] Williams was unanimously confirmed by the Senate in a voice vote on November 10, 1999, making her the first judge of color on the Seventh Circuit and the third woman of color to serve on any United States Court of Appeals.

[8] In 2010, Williams became a recipient of the 28th Annual Edward J. Devitt Distinguished Service to Justice Award.

"[9] In an article in the Chicago Tribune on December 11, 1999, Williams declined to say whether she is a Republican or a Democrat, instead calling herself politically independent: "I've written on thousands of cases across the board, and I think it would be hard to type me," she said.