He later joined the staff of Congressman Leslie C. Arends and served as a confidential assistant and chief speechwriter for Secretary Earl Butz.
[1] In the 1976 general election, McMillan defeated chairman of the Mercer County Board of Supervisors and Democratic candidate Walter E. "Red" Medhurst.
During the 80th Illinois General Assembly, he was a member of the Committees on Appropriations II; Elections and Reapportionment; and Agriculture, Conservation and Energy.
[1] McMillan ran for U.S. Congress in 1982 on a conservative platform and defeated moderate Republican incumbent Tom Railsback.
In 1988, McMillan then attempted a political comeback by running for an open seat in the Illinois House of Representatives, but was defeated by Democratic candidate Bill Edley in the Republican leaning district.