 At his wedding in 1974, Marshall III and his brother, E. Pierce Marshall, were each given shares representing a 4% stake in Koch Industries by their father, J. Howard Marshall II, who said "these are the crown jewels, take care of them.”

In 1980, the 4 sons of Fred C. Koch fought over control of Koch Industries, founded by their father.Marshall III sided with Bill Koch and Frederick R. Koch, while J. Howard Marshall II and E. Pierce Marshall sided with Charles Koch and David Koch.Charles and David got control of the company in 1983.