Jonja was born in Ho-Chi-Minh City, Vietnam and grew up in Berlin, Germany where he received classical piano lessons from Chie Muto-Kumai at the age of 4, and later studied with Gesine Tiefuhr-Disselhorst.

As early as middle school, Jonja began conducting and co-leading the senior orchestra. Throughout his middle and high school career, he conducted, arranged, musical directed, and played piano/keyboards/drums & percussion for various musical theater productions. He completed the International Baccalaureate Bilingual Diploma in 2017 and holds the ECIS Award for International Understanding.

Jonja holds a Bachelor of Arts in jazz piano and theater & performance from Bard College. Under the jazz program, he received instruction from Larry Ham and John Esposito, and conducting lessons from James Bagwell (The Orchestra Now, The American Symphony Orchestra). Jonja is a recent graduate (Cycle 33) from NYU Tisch School of the Arts and earned a Master of Fine Arts in the Graduate Musical Theater Writing Program.

​Since 2020, Jonja has volunteered as the Music Assistant for the Broadway Cares/Equity Fights AIDS annual benefit concert Broadway Backwards. The concerts were lead by Music Supervisors Mary-Mitchell Campbell (Encores, Mean Girls, The Prom, Tuck Everlasting) and Ted Arthur (Back To the Future, Diana: A New Musical, The Prom). As a music director and pianist, has performed at venues such as 54 Below, Greenroom 42, and The Fisher Center at Bard,.

His most recent shows include The Silver Child (music by Jonja Merck, lyrics by Trevor K. Band), Show & Tell, Something Rotten, Dogfight, The Gauntlet, Songs For A New World, The Last Five Years, as well as many other shows. His original musical An Artist, Now (music by Jonja Merck, lyrics by Laila Perlman) was performed at the Fisher Center at Bard College in February 2022. He is currently working on a new original musical, Lotus & Jasmine with lyricist Sravya Saraswatula (NYU GMTWP cycle 33). A new TYA musical (working title Jazzipillar) is in development with lyrics and book by Hannah Z. Morley.

Jonja’s works “Moonlight” (solo piano) and “Berlin!” (lyrics by Sravya Saraswatula) have been selected for the Apollo Global Music Awards 2025. He is the recipient of the Margaret Creal Shafer Award in Composition from Bard College, 2022.

Jonja is a proud member of MUSE (Musicians United for Social Equity) and has been a mentee in the MUSE One-On One mentorship program since 2021 (Mentors: Andrea Grody - The Band's Visit, Tootsie, and Suffs; Elizabeth Doran - Water For Elephants, SIX, Mean Girls; and Adam Beskind - Water For Elephants, Death Becomes Her). He is also a member of the Dramatist Guild of America and GEMA.