Mario Melgar is trained in Pediatric Infectious Diseases, working as a physician in two national hospitals, heading the pediatric infectious diseases department. In academia, he has coordinated the first Pediatric Infectious Diseases fellowship in the country for the past 8 years.
In research he has participated in several epidemiological studies and clinical trials, currently serving as director of a private research center.

He was president of the Infectious Diseases Society of Guatemala in 2014-2015. He has been a member of his local NITAG from its conformation in 2013 , serving as president of the committee from 2017 to 2021.