Background
Magnussen was born in Woodhaven, Queens, New York, the son of Daina, an aerobics instructor, and Greg Magnussen, a professional bodybuilder and kickboxer. He grew up in Woodhaven until the age of 10, when he moved with his family to Cumming, Georgia.
Education
Magnussen graduated from South Forsyth High School in 2003 and later graduated from the North Carolina School of the Arts.
Career
He has two younger brothers. Stage In 2007, he made his Broadway stage debut in The Ritz, starring Rosie Perez. In 2012, he was cast as Spike, alongside David Hyde Pierce and Sigourney Weaver, in Christopher Durang"s Vanya and Sonia and Masha and Spike, premiering at the McCarter Theatre in Princeton, New Jersey prior to its move to Lincoln Center in New York City.
lieutenant then moved to the John Golden Theatre, where it was nominated for six Tony Awards.
In 2014, he starred Office-Broadway with Anna Gunn in a critically acclaimed production of Sex With Strangers directed by David Schwimmer at Second Stage Theatre. J. Magnussen once was the bass player and a contributing songwriter for the New York City–based rock band The Dash, which also included Justin Ettinger (vocals), Nick Fokas (guitar), Peter Bourquin (guitar), and Alex Pappas (drums).
Currently, Billy plays guitar in the New York City-based band Reserved for Rondee, composed of Tom Degnan (bass), Nick Fokas (guitar), Warren Hemenway (drums), and Trevor Vaughn (lead vocals).