Elected as a Democrat to the Forty-fifth United States Congress, Lockwood served one term as the representative for New York's 32 District. He also served as a delegate to the Democratic National Convention in 1880, 1884, and 1896. At the 1884 Convention, Lockwood nominated Grover Cleveland for President.
Lockwood served a United States District Attorney for the Northern District of New York from 1886 until 1889 before returning to Congress from 1891 through 1895. In 1894 he decided not to run for reelection, but instead he became an unsuccessful candidate for the Lieutenant Governor of New York.
After the end of his political career he resumed his law practice before serving as the general manager from New York at the Pan American Exposition in 1901, the site of William McKinley's assassination. In 1903 Lockwood was appointed to the New York State Lunacy Commission, a position which he held until his death. He is interred at the Forest Lawn Cemetery, Buffalo, NY.
He was the father of Thomas B. Lockwood.