For all of his working life, Marshall was involved with transportation and the labor movement. As a bus driver in Louisiana and Detroit, he became a leader of the Amalgamated Transit Union, rising through union ranks to become president of the Michigan AFL-CIO for 12 years (1971-1983). In 1967, he helped organize and lead the Southeastern Michigan Transportation Authority, the first such agency in the region, and served as its chairman for nearly three years. He led in dedicating a portion of the state gas tax to public transportation. As a member and as chairman of the first State Transportation Commission (1979-1991), he remained a strong advocate for public transit and transportation workers and helped develop transportation programs for all travel modes throughout Michigan.