He attended school at Gilmanton Academy and later in East Andover, New Hampshire.

After a brief career teaching in several different New Hampshire towns, he relocated to Sauk Rapids, Minnesota, in 1855.

In 1861 he was named the head of the United States General Land Office in St.

During this time Gilman also explored the timber and mining industries, pursuing interests in Minnesota as well as Ontario and further west.

During both terms, Gilman was heavily involved in legislation surrounding railroads and supported the development of the Great Northern Railway (U.S.).