In 1924, Marshall graduated "magna cum laude" from Syracuse with a Bachelor of Science degree in forestry, finishing 4th of 59 at the College of Forestry. The senior yearbook described him as "the Champion Pond Hound of all time, a lad with a mania for statistics and shinnying mountain peaks, the boy who will go five miles [8 km] around to find something to wade thru. And the man who is rear chainman for Bob will have to hump or get wet, and probably both." By 1925, he earned a Master's degree in forestry from Harvard University.