In the past, art historians, for various reasons, have sometimes cast doubt on the existence of Hubert Van Eyck. Today, however, no one still seriously claims that the elder brother of Jan, Lambert and Margareta Van Eyck never existed. He was born at Maeseyck, near Mons, though the date of his birth is unknown. The name Hubert itself, which was not common in Ghent, may well indicate his foreign origin. A few facts can be gleaned from his tombstone, which is now in the Lapidary Museum in St Bavo's Abbey. An inscription engraved on a copper plate which has since disappeared but which was once affixed to the stone, recorded 18 September 1426 as the date of his death. However, the most crucial piece of information to have come down to us is the quatrain inscribed on the frame of the Adoration of the Lamb, the Van Eyck brothers' most celebrated work. The verse was placed there when the altarpiece was installed on 6 May 1432. It states that the polyptych was begun by Pictor Hubertus Eyck, and finished by his brother Jan, at the request of Jodocus Vyd, deputy burgomaster of Ghent, warden of the church of St John, and of his wife, Isabelle Borluut, who commissioned it. The quatrain was discovered in 1823. Although its authenticity was once contested it is now generally recognized as genuine.

An additional argument for the existence of Hubert is provided by a stylistic analysis of the painting, in which the work of two different hands can be clearly discerned. The overall conception of the altarpiece is certainly the work of Hubert, along with the execution of certain parts, such as the panels in the lower tier. Here, the manner is archaic, and reflects the continuing dominance of the international style that was practised by Broederlam. The composition is typically unoriginal: the landscape is still conceived as a distant background, with which the figures at the front have no organic relation, an effect that is reinforced by the bird's eye point of view.

According to tradition, Jan Van Eyck was also born at Maeseyck; but we can only vaguely conjecture the date of his birth on the basis of much later biographical information. Nor do we know anything of his artistic training. What we do know is that he entered the service of John of Bavaria, Count of Holland and of Zeeland, and Prince-Bishop elect of Liège, as a painter and honorary equerry. With his many assistants, he worked at the Binnenhof in The Hague. After his protector's death, he entered the service of Philip the Good on 19 May 1425. He settled in Lille - which, together with Brussels and Ghent, was part of the central administrative structure of the Duchy of Flanders and Burgundy - some time before 2 August 1425. On 26 August 1426, the painter - who was already well-known for his spirit of adventure - was paid to undertake a lengthy pilgrimage-cum-secret mission for the Duke. On 27 October of the same year he received money from the same source again, this time for "certain distant and secret journeys".

Some of these payments may also have related to an embassy the painter undertook to Valencia in Spain in 1426. His task on that occasion was to ask Alfonso V of Aragon for the hand of his niece Isabella of Urgel on behalf of Philip the Good. Jan Van Eyck's presence in Aragon would seem to be proved by the interest Alfonso subsequently took in his painting. The Spanish King bought several works from him and, between 1431 and 1436, sent his official painter, Luis Dalmau, to Flanders to study with Van Eyck. He wanted Dalmau to learn the secrets of oil painting which at that time the artists of Burgund tended to think of as their exclusive privilege. When negotiations in Valencia came to nought, Philip the Good then sent an embassy to Portugal to request the hand of the infanta Isabella in marriage. A contemporary report confirms that the painter Jan Van Eyck took part in this mission as well. Van Eyck painted two portraits of the Portuguese princess at the castle of Aviz in January 1429. Messengers then conveyed these portraits to Philip the Good. Travelling by sea and by land, they managed to reach Flanders by 1 February. Van Eyck's journeys must have contributed in no small way to the growing interest in Flemish painting that was evinced by the courts, nobility and bourgeoisie of Portugal and Spain.

He also undertook a highly confidential mission beyond the confines of Christian Europe, as part of Philip the Good's plans for a crusade. We will probably never know anything for certain of the content of Jan Van Eyck's "secret missions". But it seems possible that he was sent to reconnoitre Muslim roads and territories in southern Spain and perhaps even further afield. He would then have been expected to produce maps that could later be used for military intelligence. All we know for sure is that he was valued by the States of Burgundy not only as an exceptional painter, but also as a distinguished diplomat, and even, on occasions, as a skilled spy.

After many adventures, both artistic and diplomatic, Jan Van Eyck at last tired of his foreign missions. In 1432 he bought a house in Bruges and, at about the same time, he married a certain Margareta. The time had now come to live and paint in peace. A first child was born to the couple in 1434. The Duke of Burgundy did not forget this most loyal of artists and over the years sent Van Eyck many presents on the occasion of each successive addition to the family. An account survives for the expenses of Van Eyck's funeral, which was held in the church of St Donatian in Bruges. Since the church was closed for worship as of 23 June 1441, it seems likely Van Eyck died shortly before this date. He was regarded as a member of the Duke's family, and was thus entitled to the exceptional privilege of burial in the cloister beside the church. The following year, his brother Lambert arranged for his tomb to be moved inside the church. Although we do not know the date of his birth, his biographers have always supposed than Jan Van Eyck died young.

Beside the Ghent altarpiece, equally famous is the wedding portrait of Giovanni Arnolfini and his wife (1434; National Gallery, London), which the artist signed "Johannes de Eyck fuit hic 1434" (Jan van Eyck was here), testimony that he witnessed the ceremony. Other important paintings are the Madonna of Chancellor Rolin (1433-34 Louvre, Paris) and the Madonna of Canon van der Paele (1436; Groeningen Museum, Bruges).