James McIlhany Thomson (August 9, 1924 – July 24, 2001) was a member of the Virginia House of Delegates representing Alexandria from 1956 to 1977.

A member of the Byrd Organization, Thomson became the Virginia House Democratic floor leader, a position which he held until 1977.

[1] Thomson attended St. James Episcopal School in Hagerstown, Maryland, then served in the United States Marine Corps in World War II.

Among the laws then passed were seven directed against the NAACP and other organizations challenging racial segregation within the Commonwealth, drafted by fellow lawyer and state Senator Charles R. Fenwick of Arlington (one of the school districts being sued).

After most local schools reopened and segregation became less popular in 1961, Thomson survived a primary challenge from Dennis K. Lane.

When Alexandria won an additional seat because of the United States Supreme Court decision in Davis v. Mann (brought by other northern Virginia legislators against reapportionment by the Byrd Organization dominated legislature), he would be joined in the legislature by another Democrat with a very different political philosophy, Marion Galland, the first woman elected to represent the historic city in the Virginia General Assembly.