Guillaume Dufay was a Franco-Flemish composer and music theorist of the early Renaissance. As the central figure in the Burgundian School, he was the most famous and influential composer in Europe in the mid-15th century, and can be considered as the founding member of the Netherlands school which dominated European music for the next 150 years.

From the evidence of his will, Guillaume Dufay was probably born in Beersel, in the vicinity of Brussels. He was the illegitimate child of an unknown priest and a woman named Marie Du Fayt. Marie moved with her son to Cambrai early in his life, staying with a relative who was a canon of the cathedral there. Soon Dufay's musical gifts were noticed by the cathedral authorities, who evidently gave him a thorough training in music; he studied with Rogier de Hesdin during the summer of 1409, and he was listed as a choirboy in the cathedral from 1409 to 1412. During those years he studied with Nicolas Malin, and the authorities must have been impressed with the boy's gifts because they gave him his own copy of Villedieu's Doctrinale in 1411, a highly unusual event for one so young. In June 1414, at the age of only 16, he had already been given a benefice as chaplain at St. Gery, immediately adjacent to Cambrai. Later that year he probably went to the Council of Konstanz, staying possibly until 1418, at which time he returned to Cambrai.

From November 1418 to 1420 he was a subdeacon at Cambrai Cathedral. In 1420 he left Cambrai again, this time going to Rimini, and possibly Pesaro, where he worked for the Malatesta family. Although no records survive of his employment there, several compositions of his can be dated to this period; they contain references which make a residence in Italy reasonably certain. It was there that he met the composers Hugo and Arnold de Lantins, who were among the musicians of the Malatesta household. In 1424 Dufay again returned to Cambrai, this time because of the illness and subsequent death of the relative with whom his mother was staying. By 1426, however, he had gone back to Italy, this time to Bologna, where he entered the service of Cardinal Louis Aleman, the papal legate. While in Bologna he became a deacon, and by 1428 he was a priest.

Cardinal Aleman was driven from Bologna by the rival Canedoli family in 1428, and Dufay also left at this time, going to Rome. He became a member of the Papal Choir, serving first Pope Martin V, and then after the death of Pope Martin in 1431, Pope Eugenius IV. In 1434 he was appointed maistre de chappelle in Savoy, where he served Duke Amedee VIII; evidently he left Rome because of a crisis in the finances of the papal choir, and to escape the turbulence and uncertainty during the struggle between the papacy and the Council of Basel. Yet in 1435 he was again in the service of the papal chapel, but this time it was in Florence - Pope Eugenius having been driven from Rome in 1434 by the establishment of an insurrectionary republic there, sympathetic to the Council of Basel and the Conciliar movement. In 1436 Dufay composed the festive motet Nuper rosarum flores, one of his most famous compositions, which was sung at the dedication of Brunelleschi's dome of the cathedral in Florence, where Eugenius lived in exile.

During this period Dufay also began his long association with the d'Este family in Ferrara, some of the most important musical patrons of the Renaissance, and with which he probably had become acquainted during the days of his association with the Malatesta family; Rimini and Ferrara are not only geographically close, but the two families were related by marriage, and Dufay composed at least one ballade for Niccolò III, Marquis of Ferrara. In 1437 Dufay visited the town. When Niccolò died in 1441, the next Marquis maintained the contact with Dufay, and not only continued financial support for the composer but copied and distributed some of his music.

The struggle between the papacy and the Council of Basel continued through the 1430s, and evidently Dufay realized that his own position might be threatened by the spreading conflict, especially since Pope Eugenius was deposed in 1439 by the Council and replaced by Duke Amedee of Savoy himself, as Pope (Antipope) Felix V. At this time Dufay returned to his homeland, arriving in Cambrai by December of that year. In order to be a canon at Cambrai, he needed a law degree, which he obtained in 1437; he may have studied at Turin University in 1436. One of the first documents mentioning him in Cambrai is dated December 27, 1440, when he received a delivery of 36 lots of wine for the feast of St. John the Evangelist; how long it took to drink them is not known.

Dufay was to remain in Cambrai through the 1440s, and during this time he was also in the service of the Duke of Burgundy. While in Cambrai he collaborated with Nicolas Grenon on a complete revision of the liturgical musical collection of the cathedral, which included writing an extensive collection of polyphonic music for services. In addition to his musical work, he was active in the general administration of the cathedral. In 1444 his mother Marie died, and was buried in the cathedral; and in 1445 Dufay moved into the house of the previous canon, which was to remain his primary residence for the rest of his life.

After the abdication of the last antipope (Felix V) in 1449, his own former employer Duke Amedee VIII of Savoy, the struggle between different factions within the Church began to heal, and Dufay once again left Cambrai for points south. He went to Turin in 1450, shortly before the death of Duke Amedee, but returned to Cambrai later that year; and in 1452 he went back to Savoy yet again. This time he did not return to Cambrai for six years, and during that time he attempted to find either a benefice or an employment which would allow him to stay in Italy. Numerous compositions, including one of the four Lamentationes that he composed on the fall of Constantinople in 1453, his famous mass based on Se la face ay pale, as well as a letter to Lorenzo de'Medici, survive from this period: but as he was unable to find a satisfactory position for his retirement, he returned north in 1458. While in Savoy he served more-or-less officially as choirmaster for Louis of Savoy, but he was more likely in a ceremonial role, since the records of the chapel never mention him.

When he returned to Cambrai for his final years, he was appointed canon of the cathedral. He was now the most renowned composer in Europe. Once again he established close ties to the court of Burgundy, and continued to compose music for them; in addition he received many visitors, including Busnois, Ockeghem, Tinctoris, and Loyset Compere, all of whom were decisive in the development of the polyphonic style of the next generation. During this period he probably wrote his mass based on L'homme arme, as well as the chanson on the same song; the latter composition may have been inspired by Philip the Good's call for a new crusade against the Turks, who had recently captured Constantinople. He also wrote a Requiem mass around 1460, which is lost.

After an illness of several weeks, Dufay died on November 27, 1474. He had requested that his motet Ave regina celorum be sung for him as he died, with pleas for mercy interpolated between verses of the antiphon, but time was insufficient for this to be arranged. Dufay was buried in the chapel of St. Etienne in the cathedral of Cambrai; his portrait was carved onto his tombstone. After the destruction of the cathedral the tombstone was lost, but it was found in 1859 (it was being used to cover a well), and is now in a museum in Lille.