Forrest C. Donnell (August 20, 1884–March 3, 1980) was a United States Senator and a Governor of Missouri. He was a Republican.

Donnell was born in Quitman, Missouri. He graduated from the University of Missouri at Columbia in 1904 and from its law school in 1907. He was the city attorney of Webster Groves, Missouri, a city west of St. Louis.

He served as the Governor of Missouri between 1941 and 1945. He was elected to the U.S. Senate and served from 1945 to 1951, but was an unsuccessful candidate for reelection in 1950. He died in 1980 at the age of 95 in St. Louis.