Bennet was a lawyer in private practice and an official reporter of the Orange County Board of Supervisors from 1892 to 1893. He was a member of the New York State Assembly (New York County, 21st District) in 1901 and 1902. He served as justice of the municipal court of New York, New York, 1903. He served as member of the United States Immigration Commission from 1907 to 1910 and was one of two (of fourteen) members that generally opposed the restriction of immigration. He served as delegate to the Republican National Convention in 1908 and 1916. Bennet also spoke out against the denial of civil rights to African Americans in southern states, noting that those states benefited from greater representation because of the size of their black population but prevented those black citizens from voting.