He competed for the United States in the 1908 Summer Olympics held in London, Great Britain, where he won the bronze medal in the Marathon.

At the 1906 Intercalated Games in Athens, he finished in twelfth place, and at the 1912 Summer Olympics in Stockholm, he was 10th in the event.

On May 6, 1905, Forshaw beat Sidney Hatch and Felix Carvajol to win the Missouri Athletic Club's All-Western Marathon in a time of 3:15:58.

[2] In March, 1912, Forshaw was one of "twenty of the best distance runners in the middle west" scheduled to participate in a 20-mile indoor marathon at Riverview Rink in Chicago, Illinois.

[3] He also finished second to Joseph Erxleben in the 25-mile Missouri Athletic Club marathon in St. Louis on May 4, 1912 to earn a spot on the United States Olympic Team.