Abelgas was born to a poor family. His father worked as a driver and his mother worked as a laundry worker. Their family lived as illegal settlers in San Andres, Manila during his youth. At a young age, Abelgas worked as a newspaper boy to help his family.[2]
For his collegiate studies, Abelgas pursued a bachelor's degree in journalism at the Lyceum of the Philippines University in Manila. Abelgas also finished law studies but he was not able to pass the bar examination.[2]
Abelgas joined ABS-CBN as early as 1987 as a member of the TV Patrol news team. He covered various natural disasters and events such as the 1991 eruption of Mount Pinatubo. Abelgas later shifted his focus to investigative journalism.[1]
He covered crimes as an anchor in True Crime and Private I.[3] In S.O.C.O. (Scene of the Crime Operatives), he worked with police and interviewed crime witnesses.[1] He also communicates with convicted and suspected criminals as part of his work in S.O.C.O. Of his own approach, Albegas said he talks with the suspect calmly. He has received death threats from people whom he helped imprison – this became frequent that Abelgas no longer finds it bothersome.[4]
On July 15, 2023, Abelgas returned to television after a 3-year hiatus, after he transferred to TV5 a few days before. He is currently hosting the program Gus Abelgas Forensics, which is similar to his previous program, S.O.C.O. It airs on TV5, One PH and RPTV with a radio simulcast via 92.3 Radyo5 True FM.