Lucas Horenbout, often called Hornebolte in England, was a Flemish artist who moved to England in the mid-1520s and worked there as "King's Painter" and court miniaturist to King Henry VIII from 1525 until his death. He was trained in the final phase of Netherlandish illuminated manuscript painting, in which his father Gerard was an important figure, and was the founding painter of the long and distinct English tradition of portrait miniature painting. He has been suggested as the Master of the Cast Shadow Workshop, who produced royal portraits on panel in the 1520s or 1530s.

Horenbout was born in Ghent, where he trained with his father, Gerard Horenbout, becoming a master of the local Guild of Saint Luke in 1512. Gerard was an important Flemish manuscript illuminator in the dying days of that art-form, who had been court painter, from 1515 to about 1522, to Margaret of Austria, regent of the Netherlands. Margaret was twice sister-in-law to Catherine of Aragon, who was married to King Henry VIII of England when the Horenbouts came to England. Gerard is sometimes identified with the "Master of James IV of Scotland", one of the many artistic personalities identified as a significant illuminator in the Ghent-Bruges school of the period, to whom no historical person can be attached.

Horenbout came over to England at an unknown date with, or perhaps before, his sister Susannah Hornebolt and his father. It has been suggested that their move was in connection with an attempt by the King, or possibly Cardinal Wolsey, to revive English manuscript illumination by establishing a workshop in London, but this is controversial. In about 1525 he married Margaret Holsewyther who was an artist of German descent who had probably been born in England.

His father Gerard is first recorded in England in 1528, and later returned to the Continent, probably after 1531; he had died in Ghent by 1540. Susanna, who was also an illuminator, is recorded in 1529 as married to a John Palmer and in England. Lucas is documented in England from September 1525, when he was first paid by the King as "pictor maker". By 1531 he was described as the "King's Painter", and this appointment was confirmed for life in June 1534, when he became a "denizen" - effectively a naturalised citizen. Horenbout was very well paid, at sixty-two pounds and ten shillings (but only thirty-three pounds and six shillings according to Richard Gay) per year, a "huge" sum according to Strong, and better than Holbein's thirty pounds a year in his period as Henry's court painter. He was granted a "tenement" in Charing Cross, and permitted to take on four foreign journeyman. Lucas died in London, and was buried at Saint Martin in the Fields and left a wife and daughter, Margaret and Jacquemine. Margaret's sales included being paid sixty shillings three years later by Queen Catherine Parr for some paintings.

Margaret is credited with a number of paintings during his lifetime and one of Catherine Parr was attributed to him but it was painted after his death. He had left his studio to be unequally divided between his wife and his daughter. For many years his studio was paid by Catherine Parr for miniatures that his wife presumably created.