Senator Juan Gaerlan was born in Tagudin, Amburayan, Ilocos Sur on July 7, 1884 to Sabas Gaerlan and Rosalina Lorenza.
He was interpreter and deputy treasurer of Bontoc (1905); Clerk deputy treasurer, and assistant post master, Bontoc, (1906-08); deputy provincial treasurer, mining recorder and traveling deputy treasurer, Bontoc (1910-1912); assistant agricultural inspector, bureau of Agriculture (1913-1916); Agricultural inspector and farm adviser, same bureau, (1916-1920); deputy governor-at-large, Mountain Province (1920-1921); acting deputy governor of Apayao and Benguet (1921-1922); and deputy governor of Benguet (1923-1931).
He was appointed Representative for the Mountain Province (1931-1934) and later, Senator for the 12th Senatorial District comprising Mt. Province, Baguio, Nueva Vizcaya, Agusan, Bukidnon, Cotabato, Davao, Lanao, Sulu and Zamboanga. (1934-1935).