Born around 1385, Dunstable was the most influential English composer of his day. Very little is known conclusively about his life, but through manuscripts and records, it is possible to piece together his possible patrons. It is believed he was in the service of John, Duke of Bedford (Henry V's brother), who was regent in France from 1422 to 1435. After Bedford's death in 1435 he was probably in the service of Joan, Dowager Queen of Henry IV. He received a substantial payment from her in 1436. She died in August 1437, and Dunstable was known to be in the service of Humphrey, Duke of Gloucester (another brother of Henry V) at least from July 1438.
Dunstable probably followed Bedford to France and his music was very well known there. The extensive English possessions in France explain the number of English musicians there at this time, and the widespread dissemination of their music throughout the continent. There is evidence that Dunstable wrote the music for the marriage of Henry V to Catherine of Valois, and also possibly the music for Henry VI's coronation in Paris in 1431.

English Medieval music had a great emphasis on thirds and sixths, and for full bodied textures, making their music harmonious, compared to the more dissonant continental tradition. Dunstable's sonorous melodies were copied by French composers, and the style became known as contenance angloise or English manner. It has been said that Dufay owed his superiority to Dunstable. He incorporated the "English manner" into continental music, creating a style more graceful and expressive. Despite his great influence on continental composers, some musicologists say Dunstable has been accredited personally with the accomplishments of the English school as a whole. Tinctoris described him as "primus inter pares" (first among equals).

There are only about 50 surviving works definitely ascribed to Dunstable. Other works, particularly of the English carol repertory, are labeled as either anonymous or sometimes "de Anglia", but are probably by Dunstable. There is no way to be definite until corroborative evidence is discovered. Stylistic analysis is usually not helpful for works of this period, as it is not easy to distinguish between Dunstable and other English composers of his time. Even on some works that bear Dunstable's inscription, musicologists are not sure. Also, precise dating of his pieces is almost impossible, so it is difficult to describe his development with musical styles and forms. It is clear, however, that he composed in all the principle types and styles of polyphony of his time. About one third of all his surviving works are sections of the Ordinary of the mass, but only a few secular songs are attributed to him.