Gaerlan was born in San Juan, La Union on December 19, 1958.[1] He obtained his law degree from the San Beda College of Law.[1] Gaerlan served as a Public Attorneys' Office lawyer before becoming a municipal trial court judge in Bangar, La Union and later as a regional trial court judge in Branch 26 of San Fernando, La Union and Branch 92 of Quezon City. He was appointed as a Court of Appeals justice in 2009.[2]
In 2017, Gaerlan was nominated and interviewed for the seat vacated by Jose C. Mendoza, but was not shortlisted.[2] On January 8, 2020, President Rodrigo Duterte chose Gaerlan over five shortlisted candidates and was appointed to the court to fill the seat vacated by Diosdado Peralta.[3]
