Born in Raleigh, North Carolina, Cantwell was the son of an Irish-born military officer who sent him to study at a Roman Catholic seminary in Ireland.

Under the command of Captain Michael A. Healy, the Thomas Corwin made summer patrols to the Bering Sea and Alaskan coast in both 1884 and 1885.

He subsequently published "Report on the Operations of the United States Revenue Steamer Nunivak on the Yukon River Station, 1899–1901".

[5] Cantwell was promoted to senior captain during World War I, serving as commanding officer of the San Pedro Coast Guard training center.

[7] Cantwell died at a Marin County hospital in Sausalito and was buried in the Pacific Ocean from the Thetis-class cutter USCGC Daphne on 10 October 1940.