Rosenthal graduated from North Plainfield High School in 1998 in North Plainfield, New Jersey and attended college at Rutgers University in New Brunswick, New Jersey where he studied history and political science. He graduated from Rutgers University in 2003 with a degree in history.
Rosenthal was around the age of 6 years old when his mother took him into New York City to audition for an acting agent and they liked him enough to send him out on some auditions. He acted in several commercials as a child starting at the age of 7. He claims that acting was something his parents dragged him to do more or less, but around the beginning of 9th grade he realized that acting was something he truly wanted to do. Gerry has appeared in numerous television commercials and radio voice-overs, along with television series including TV's Law & Order and Law & Order: Special Victims Unit, as well as the films Liberty Heights, Finding Forrester, and Wirey Spindell. Gerry also provided the voice for the main playable character Jimmy Hopkins in the 2006 video game Bully, from Rockstar Games. After this he decided to quit acting.
Rosenthal's father began teaching him guitar and piano around the age of 7. Between the ages of 10–13 he attended the St. Thomas Choir School in New York City, a boarding school for young male choristers, where he sang 5–6 church services a week at St. Thomas Church Fifth Avenue with the St. Thomas Choir of Men and Boys under the direction of Dr. Gerre Hancock. While at St. Thomas, Gerry studied piano with concert Pianist Leslie Singer and music theory with Composer Scott Eyerly (composer of the Opera house of Seven Gables, as well as a faculty member at The Juilliard School.) He was fortunate enough to tour extensively with the St. Thomas Choir, traveling to Austria, Italy, Vienna, and Ireland. In high school Gerry continued his piano studies privately with Paul Salamone, a jazz Pianist from Scotch Plains, New Jersey. While earning a History degree at Rutgers University, Gerry attended a semester at Berklee College of Music in Boston, Massachusetts where he studied guitar privately with John Marasco (Eartha Kitt, Al Martino) and John Thomas (Kenny Drew, Tony Scott, Roy Haynes) as well as music theory with Jim Stinnett (bass instructor for Mike Gordon of Phish.) While in college he also studied privately on guitar with Karl Cochran (Ace Frehley, Joe Lynn Turner.) And he always played with different groups for fun in college, so within 6 months of moving home He was playing in about 4 different bands in the New Brunswick NJ music scene. It happened slowly, but over the years his focus gradually shifted more and more towards music, to the point where that's how he makes his living today. He claims he still goes on acting auditions, but music is his life at this point.