Justin was born and raised in Brooklyn.
The son of a record salesman and early childhood educator. After attending PS 185, McKinley JHS and Xaverian High School, Brannan studied journalism at Fordham, before embarking on a career as a professional musician. His bands released several albums and toured the world – traveling to over fifty countries across five continents.
While working at a New York City radio station, Brannan got involved in union organizing and fought to recover unpaid wages for his co-workers. He then served as Chief of Staff to his predecessor Councilman Gentile and Director of Intergovernmental Affairs at the Department of Education where he helped oversee the expansion of Universal Pre-K.