He was appointed to the court on August 26, 2002, by President Gloria Macapagal Arroyo, and served until his mandatory retirement on April 27, 2007.

Born in Santa Lucia, Ilocos Sur, Callejo Sr. worked with the government for 37 years, serving the Judiciary as magistrate at three court levels.

As his 21 years of service in the judiciary drew to a close midnight on April 28, 2007, he was acclaimed by his colleagues for “his untarnished reputation for honesty and integrity, which lawyers and judges, present and future, should emulate.” He was a Philippine Judicial Academy Professor, and was its Vice-Chancellor in 2015, and Chairperson of the Department of Criminal Law from 1998 until his death.

[6] His wake was held at Loyola Memorial Chapels funeral home along Commonwealth Avenue from September 20-23.

On September 22, at 4:00 P.M., Alexander Gesmundo, Diosdado Peralta, Lucas Bersamin and Angelina Sandoval-Gutierrez led the eulogy in the solemn necrological service.