Born in Cap-Haïtien in 1909, Monestime studied rural medicine and wrote three books on the subject. In 1937, he was one of the only doctors on duty during the Parsley Massacre, and was subsequently awarded the Haitian Legion of Merit for his work during that crisis.
He moved to Quebec City in the 1940s. After upgrading his medical training he planned a move to Timmins, Ontario to set up a medical practice, but when he stopped in Mattawa en route, he was convinced by a restaurant owner to stay in that town and set up practice there instead. He married Zena Petschersky, an immigrant from Danzig, whom he met in Ottawa in 1953.
Monestime practiced medicine in Mattawa until 1964, when he was elected the town's mayor. Except for one year that he took off for personal reasons, he remained mayor until his death in 1977.
Monestime was very active with the Progressive Conservative Party of Canada, and served as its national director. He considered running federally for the party, and in 1971 he ran and lost in a bid for the presidency of the party. A Red Tory, Monestime was attracted to the party because of Prime Minister John Diefenbaker's Bill of Rights.
On February 29, 1976, Monestime's 21-year-old son, Fedia, was shot and killed outside the Trans-Canada Hotel in Mattawa. He was in a group chasing a man who had fired his rifle into the wall after a bar fight, when the man fired on them, also injuring three others. Ralph Childerhose was charged with murder and acquitted, a decision Monestime considered unjust.
Monestime and his wife established a nursing home in Mattawa in 1975. His daughter Vala Monestime Belter continues to run the home today, and has served on the boards of Ontario Northland and TVOntario.
In 2014, Frantz Liautaud, the current ambassador of Haiti to Canada, visited Mattawa for a gala celebration of the 50th anniversary of Monestime's first election as mayor.
- "Mattawa's Dr. Firmin Monestime Remembered", North Bay Nugget, October 26, 2007.
- "Visite de l’Ambassadeur à Mattawa". Embassy of Haiti in Canada.
- "... Conférences de médecine rurale (Open Library)". Retrieved October 6, 2014.
- "MONESTIME, Zenaida Feodorovna (Zena) Petschersky". BayToday.ca. Retrieved October 6, 2014.
- "Choice of president shows Tories aiming at Ontario voters". Ottawa Journal, December 8, 1971.
- Where Rivers Meet: The Story of Dr. S. F. Monestime, Doug Mackey.
- "Hotel fight leads to man's death". Ottawa Citizen. March 1, 1976. Retrieved October 6, 2014.
- Hodgson Announces New ONTC Board of Directors, June 20, 1996.
- TVOntario Annual Report 2003-04