Born in Calais, Washington County, Vermont, Gilman went to the Calais public schools and to the Washington County Grammar School in Montpelier, Vermont.

In 1844, Gilman and his wife moved to Chicago, Illinois where they lived until 1868.

In 1859, Gilman was an unsuccessful nominee for the office of mayor of Chicago, running on the Democratic ticket.

Gilman was librarian of the Vermont Historical Society from 1874 to 1881 and compiled an extensive bibliography of Vermont-related works which was collected and published after his death.

[1][2][3][4] Gilman's younger brother John M. Gilman became a lawyer and politician in St. Paul, Minnesota; his step-brother Dorman Bridgman Eaton was a lawyer in New York City well known for his work on civil service reform.