Marjon started his career in 2008 as a courtside reporter for the Philippine Basketball Association games when it was still produced by Solar TV. He was then elevated as a commentator for the radio coverage of the games. When Sports5 took over as the coverer of the PBA games in 2010, Marjon was assigned as a play-by-play commentator. He also serves as a play-by-play commentator for other basketball leagues covered by Sports5, notably for the Pilipinas Commercial Basketball League (PCBL), PBA Developmental League (PBA D-League) and for international basketball tournaments such as the FIBA Asia Championship (2013 and 2015), 2014 FIBA World Cup, and 2016 Rio Olympics among others.
- Bacnis, Justine (October 1, 2018). "Odd Sunday for Magoo Marjon as he dabbles into barker duties". Tiebreaker Times. Retrieved April 11, 2022.