Jan Thomas or Jan Thomas van Ieperen was a Flemish Baroque painter, draughtsman and printmaker. He was first active in Antwerp where he worked in the workshop of Rubens. He later became court painter at the Habsburg court in Vienna. He is known for his portraits of the rulers of Austria as well as for his pastoral, mythological and religious scenes.

Jan Thomas was born in Ypres, Flanders. Ypres is called Ieper and Ieperen in Flemish. The addition 'van Ieperen', which means 'from Ypres' was added to his name to indicate this.

Little is known about the artist's training. The 17th century Flemish biographer Cornelis de Bie wrote in his Het Gulden Cabinet that Jan Thomas was a pupil of Peter Paul Rubens. There is evidence that he spent time in Rubens' workshop at the end of Rubens' life or shortly thereafter. There are stylistic grounds to consider Thomas as a pupil of Rubens as he was familiar with Rubens' late works and translated some of them to smaller scale paintings. Modern scholarship tends to regard Jan Thomas as one of the many collaborators in Rubens' workshop who assisted with large commissions such as the decorations for the Torre de la Parada, the hunting lodge of the Spanish king (1636-1638). It is possible that upon Rubens' death Thomas was the 'primer official' of Rubens' workshop, i.e. the chief assistant in charge of executing paintings after the designs of the master.

Jan Thomas became a master in the Antwerp Guild of Saint Luke in 1639/1640. Two years later he acquired Antwerp citizenship. In 1641/1642 he took Andris Lamberechts on as an apprentice. The next year Andries de Coninck and Jacob Sons joined his workshop as pupils. In 1642 he married Maria Cnobbaert, daughter of the Antwerp book dealer Joannes Cnobbaert. In 1652 Jan Thomas' third child was baptized in the St. James' Church in Antwerp, which is evidence that he was then still living in that city.

It is believed that Jan Thomas left Antwerp in 1654 to work as a painter for the bishop of Mainz Johann Philipp von Schönborn one of the important courts at that time. Jan Baptist de Ruel was his pupil during his stay in this city. Around 1658 he was in Frankfurt at the time of the coronation of Leopold I as emperor of the Holy Roman Empire and painted a (now lost) portrait of the emperor. In that period he also received commissions from the Archduke Leopold Wilhelm of Austria. From the latter part of the 1650s Jan Thomas certainly lived with his family in Vienna. He is documented in Vienna when a child of his was baptized there on 8 December 1663. He is recorded living in the Kärtnerstrasse in 1667. In Vienna he received commissions from the imperial court and painted the portraits of Leopold I and his wife Margaret Theresa in theater costume. These portraits were made at the occasion of the celebrations surrounding the marriage of the imperial couple in 1666.

Jan Thomas also received commissions from the higher clergy and the aristocracy, such as the House of Zrinski or Zrínyi. He painted a portrait of the general and poet Miklós Zrínyi a few years before Zrínyi's death in 1664.

He died from a stroke in Vienna on 6 September 1673.