Giel Vleggaar was born on January 9, 1974 in Amsterdam. He studied jazz arranging and composition with Jurre Haanstra at the Hilversum Conservatory and classical composition with Daan Manneke and Theo Verbey at the Conservatory of Amsterdam. He has taken master classes with George Crumb, among others.
Upon finishing his studies, Vleggaar won the NOG Encouragement Prize from the Netherlands Ballet Orchestra (Holland Symfonia) for his orchestral piece Fast Lane Woodpecker. A steady stream of commissions and performances have followed since, both in the Netherlands and abroad. He has written works for the Asko Ensemble, Orkest de Volharding, the Nieuw Ensemble, the Nederlands Strijkers Gilde, the Nederlands Vocaal Laboratorium, the Doelenkwartet and the Radio Kamer Filharmonie.