Van Honthorst was born in Utrecht, the son of a decorative painter, and trained under his father, and then under Abraham Bloemaert.
Having completed his education, Honthorst went to Italy, where he is first recorded in 1616. He was one the artists from Utrecht who went to Rome at around this time, all of whom were to be deeply influenced by the recent art they encountered there. They were named the Utrecht caravaggisti. The other three were Dirk van Baburen, Hendrick ter Bruggen and Jan van Bijlert. In Rome he lodged at the palace of Vincenzo Giustiniani, where he painted Christ Before the High Priest, now in the National Gallery, London. Giustiniani had an important art collection, and Honthorst was especially influenced by the contemporary artists, notably Caravaggio, Bartolomeo Manfredi and the Carracci. He was especially noted for his depiction of artificially lit scenes. Cardinal Scipione Borghese became another important patron, securing important commissions for him at San Silvestro Della Mariro, Montecompatri, and at Santa Maria della Vittoria in Rome. He also worked for Cosimo II de Medici, the Grand Duke of Tuscany.