Following law school graduation, Johnson started her legal career as a private practice attorney licensed in the nation of Denmark from 1970 to 1971. During this time, Johnson also served as a part-time faculty member for the University of Copenhagen Faculty of Law.
After receiving her license to practice law in the United States, Johnson started her legal career as a private practice attorney in Alabama from 1973 to 1979. In 1978, Johnson held a part-time Municipal judge for the City Court of Muscle Shoals from 1978 to 1979. In 1979, Johnson was elected by the people of Alabama to become a Circuit court judge in the 31st Judicial Circuit Court of Alabama until her appointment to the federal bench in 1999. Johnson was the Chief Judge of the Court from 1980 to 1999.
Federal judicial service
On the recommendation of U.S. Senator Richard Shelby, Johnson was nominated by President Bill Clinton on August 31, 1998, to a seat vacated by James Hughes Hancock. Johnson was confirmed by the Senate on October 8, 1998, and received commission on October 9, 1998. She assumed senior status on October 24, 2012.
