She was an attorney with the Civil Rights Division of the United States Department of Justice in Washington, D.C. from 1971 to 1973.

She was then an assistant United States attorney for the Eastern District of Missouri from 1973 to 1978.

During her service as a state court judge, Hamilton was an adjunct professor, teaching at Saint Louis University Law School from 1986 to 1987, and in 1989, and at Washington University School of Law from 1987 to 1992.

[1] On August 3, 1990, President George H. W. Bush nominated Hamilton to a seat on the United States District Court for the Eastern District of Missouri vacated by Judge John Francis Nangle.

She was confirmed by the United States Senate on September 28, 1990, and received her commission on October 1, 1990.