Gillis Mostaert was born in
Hulst. According to the early artist biographer
Karel van Mander Gillis Mostaert was the twin brother of the painter
Frans Mostaert and the grandson of the painter
Jan Mostaert. Modern scholarship casts doubt on the statement that Jan Mostaert was a relative of Gillis. While his brother Frans became a pupil of the landscape painter
Herri met de Bles, according to van Mander, Gillis studied landscape painting with
Jan Mandijn although there is no record in the Guild books documenting such apprenticeship. Van Mander recounts that both brothers joined the Antwerp
Guild of Saint Luke in 1555. It is suspected that Gillis worked along
Marten van Cleve and
Maerten de Vos in the studio of
Frans Floris, the leading Antwerp history painter of his time. Gillis Mostaert the Elder was well-respected by his fellow painters. The painters
Peeter Baltens and
Crispin van den Broeck were godfathers to his children born respectively in 1571 and 1588. Mostaert established a thriving workshop in Antwerp and his work commanded high prices in the market. These collectors included François Perrenot de Granvelle (1559–1607) (younger brother of Cardinal
Antoine Perrenot de Granvelle),
Archduke Ernest of Austria (1553–1595) and
Archduke Leopold Wilhelm of Austria. Filips van Valckenisse who was the Lord of Hemiksem, head of the Antwerp militia and perhaps Antwerp's greatest art collector owned over 50 paintings by Mostaert. He died in
Antwerp. It is believed that he was heavily indebted at the time of his death and that the contents of his workshop was sold off or distributed to creditors to pay off these debts. Many of his works were acquired by Filips van Valckenisse, lord of
Hemiksem, who still owned a number of these when he died himself in 1614. His pupils were
Gillis van Coninxloo,
Hendrik Gijsmans, Henrick Pieters and
Jan Soens. ==Work==