Joining the firm of Evart, Southmayd and Choate, Kilbreth pursued a career in commercial law. He was a member of the Democratic party, and was prominent in the municipal reform movement following the scandals surrounding
William M. Tweed. He was a member of the Irving Hall faction within the Democratic party in New York State, later joining the County Democracy, where he was a friend and consistent supporter of
Grover Cleveland. In 1873, Kilbreth was appointed to a ten-year term as a New York Police Justice by Mayor
Havemeyer. However, this appointment was delayed by a political showdown between Mayor and Aldermen: After serving a full 10-year term, much of it on the bench of the Court of Special Sessions, Kilbreth was re-appointed to the Police Bench by Mayor
Franklin Edson for a further ten-year term in 1882. By the time of the expiry of this second term the Mayor of New York was a Tammany Hall man,
Hugh J. Grant, and Kilbreth's appointment was unsurprisingly not renewed. ==Collector of the Port of New York==