Ambrosius Francken I was a Flemish painter known for his religious works and historical allegories painted in a late Mannerist style. He was a prominent member of the Francken family of artists, which played a very important role in the Flemish art scene from the late 16th to middle 17th century.

Ambrosius Francken I was born in Herentals. His father was the painter Nicolaes Francken from Herentals who later moved to Antwerp. His brothers Frans Francken I and Hieronymus Francken I both became successful painters. Ambrosius studied under his father and the leading Antwerp Mannerist painter Frans Floris. The early biographer Karel van Mander reports in the Schilder-boeck that Francken spent time in Tournai where he lived at the Bishop's residence. Van Mander met him in Tournai while he himself was residing there as a young pupil at his master Pieter Vlerick's house. In 1570 Francken spent some time in Fontainebleau.

Around 1573 Ambrosius Francken I was back in Antwerp where he joined the local Guild of Saint Luke as a master. Ambrosius lived in a very turbulent time due to the conflict between Calvinists and Catholics in the Low Countries. In 1577 Antwerp had elected a Calvinist city council. The council ordered in 1581 the systematic removal of all images from local churches. This event is referred to as the 'silent iconoclasm'. Ambrosius, who is believed to have converted to Calvinism himself, was elected dean of the Guild in 1582. After the Fall of Antwerp, the city became Catholic again and Ambrosius made it known he was Catholic again.

He clearly established a name for himself as a prolific maker of the many altarpieces that replaced the ones destroyed during the iconoclastic troubles. His reputation was such that in 1589 he together with Maerten de Vos was appointed by the Ghent magistrate to value the painting of the Last Judgment by Raphael Coxie. Raphael Coxie was involved in a dispute with the Ghent magistrate who he felt was offering a sum that was too low for his masterpiece. Ambrosius Francken and Marten de Vos were also chosen as the chief designers of the decorations for the 1594 Joyous Entry into Antwerp of the newly appointed governor of the Southern Netherlands, Archduke Ernest of Austria.

He married Clara Pickarts and later became the teacher of Hieronymus Francken II, the son of his brother Frans Francken I. He died in Antwerp.