Momoyo Koyama is a Japanese actress, voice actress, and singer born on November 30, 1995, in Sapporo, Hokkaido. She is affiliated with the talent agency Stardust Promotion and is a member of the voice actor unit SoundOrion.

Koyama's career in performance began at a young age. She became affiliated with the Sapporo-based agency Egg in 2007 and spent a decade performing in various theatrical plays in Hokkaido. A significant early milestone was her role as Sailor Mercury in the 2014 and 2015 stage musical adaptations of Pretty Guardian Sailor Moon. It was the director of these Sailor Moon musicals who, surprised to learn she was not a voice actress, encouraged her to pursue voice acting. Following this advice, she successfully auditioned for Stardust Promotion, joined the agency in 2017, and moved to Tokyo.

Her most prominent and defining role began that same year when she was cast as Karen Aijō, the protagonist of the multimedia franchise Revue Starlight. Her involvement with the character started with the franchise's stage play in 2017, and she subsequently reprised the role in the 2018 anime television series, its compilation films, and the stage play sequels. This role established her as a leading voice in a major cross-platform project.

Beyond Revue Starlight, Koyama has voiced a variety of other anime characters. These include Elma in the 2020 series Interspecies Reviewers, Kei Todo in Rebirth, and Chihori Hokuto in Teppen—!!!!!!!!!!!!!!! Laughing 'til You Cry. She has also taken on minor roles in series such as Love Live! Nijigasaki High School Idol Club and Sorcerous Stabber Orphen. Her work extends to video games, where she has voiced characters like Haruka Shima in the Onsen Musume franchise and reprised her role as Karen Aijō in the Revue Starlight: Re LIVE game.

In addition to acting, Koyama is a singer as part of the group SoundOrion. She has also contributed to theme song performances for anime like Teppen—!!!!!!!!!!!!!!! and Rebirth. In 2020, she took a brief hiatus from singing work to undergo surgery for vocal cord nodules, from which she successfully recovered and resumed her activities.