Atty. Montejo held an undergraduate degree in A.B. Philosophy from the University of the Philippines – Diliman, which he earned in 1989. He pursued his legal studies at Ateneo de Davao University’s College of Law, where he graduated cum laude in 1991. That same year, he took the Philippine Bar exams and was admitted to the bar in 1992, ranking number 12 with a grade point average of 85.500.

As a law student, Atty. Montejo was a legal intern with the Clinical Legal Education Program at Ateneo de Davao University, where he was recognized as the Outstanding Legal Intern in 1991. Following his admission to the bar, he joined the Ateneo Legal Services Office, serving as a supervising attorney until December 1998.

Atty. Montejo was part of the faculty at Ateneo de Davao University’s College of Law, where he taught constitutional and political law subjects, administrative law, and served as a reviewer for the university’s Pre-Bar Review classes. He also served two terms as director of the Integrated Bar of the Philippines – Davao City Chapter. Additionally, he was one of the legal counsels for the City of Davao during Mayor Benjamin C. de Guzman’s term and a legal consultant for the Davao City Council.

Atty. Montejo was a member of the Alpha Phi Beta Fraternity (University of the Philippines), Lakas Atenista (College of Law, Ateneo de Davao University), and the Free Legal Assistance Group (FLAG). He also pursued a master’s degree in law at San Beda University College of Law’s Davao City extension program.

Born in Davao City, Atty. Montejo’s family has roots in Cebu, with his father, the late Alejo Algones Montejo, Sr., hailing from Argao, and his mother, Rosalina Agdon Letrondo, from Cebu City. He had two children, Paolo Chirho and John Paul.