Neil was born on June 14, 1901, at Rose Hill, New York. He attended Syracuse University and received an AB degree with Phi Beta Kappa in 1922 and an AM degree in 1924. He joined the Bureau of Plant Industry as a junior botanist in 1924 and went plant collecting in Newfoundland in 1925, returning to become a graduate assistant at Cornell University in 1925 to 1926. He became a Museum Assistant in botany at the New York State Museum from 1926 to 1927 and an instructor in botany at University of Minnesota from 1927 to 1928. He returned to Washington as assistant biologist in the U.S. Biological Survey starting in 1929 and later a botanist with the U. S. Fish and Wildlife Service at the Patuxent Wildlife Research Center, specializing in marsh ecology and retiring in 1971. During his tenure at Patuxent he developed guides for identification of wetland plants, which were later reprinted by Dover Publications.
He died on September 12, 1994, in Camden, Maine.
Neil was elected to the Washington Biologists’ Field Club in 1935. He served as secretary from 1944 to 1950, president from 1951 to 1954, and terminated his membership in 1964.