Thomas Crain accompanied his father to Italy but returned in 1881, and began the study of law.

Grant appointed him as his private secretary, and in February 1890 as City Chamberlain to succeed Richard Croker who had resigned.

He was Tenement House Commissioner from 1904 to 1905 when he resigned following a dispute with Mayor George B. McClellan Jr. in the wake of a fire at 105 Allen Street that killed 18 people, mostly children.

He was the presiding Judge in the 1911 trial of Triangle Shirtwaist Factory owners Max Blanck and Isaac Harris.

He convened a grand jury to look into the Arnold Rothstein murder and it adjourned saying it could not solve the case.

In 1930, he convened a grand jury to investigate job buying Magistrate George F. Ewald.