Theodoor van Loon was born in Erkelenz (present-day Germany) in 1581/82. Next to nothing is known about his early life. In 1602 he surfaces in Rome, where he lived with the Flemish painter - and friend of Rubens - Jacob de Hase. He became a member of the local painter's guild of St Luke in 1604. While in Rome, the artist had mingled with other expats from artistic and intellectual circles, befriending several of them, such as the Flemish humanist Erycius Puteanus and the German Johann Faber, the papal botanist. He also met the Antwerp-born painter and architect Wenzel Coeberger, who had lived in Rome since 1601 but returned to Brussels to work for the Archdukes Albrecht and Isabella in 1604. It was to Coeberger that van Loon owed his first commissions in the Netherlands; presumably that is why van Loon moved to Brussels in 1612 (although it has been assumed the painter already had some connections with Flanders prior to his stay in Rome). He was to return two or three times to the Eternal City, between 1617-1619 and 1628-1632. 

From 1613 onwards, van Loon worked for the Archdukes, receiving commissions from their architect, Coeberger. The cycle of paintings he made in 1616 - 1621 for Coeberger's Basilica of Our Lady of Scherpenheuvel made him a famous and widely-praised artist. Around this time, his portrait was included in van Dyck's Iconographia. Various other commissions ensued, almost exclusively for large altarpieces for churches and abbeys in and around Brussels. A few years later however, Coeberger was much less active as an architect, resulting in less work for van Loon. He was commissioned by friends for designs for frontispieces, but seems to have been restless and moved to Leuven, where his friend Puteanus lived as a professor at the university. Little is known about the end of his career. It appears van Loon never married nor had any children or even a fixed residence, making him a somewhat elusive figure for some periods of his life. In 1997, his last will and testament was discovered in Maastricht, where he died in 1649, leaving half of his not inconsiderable wealth to various catholic institutions.

It would be hard to overstate the influence of what van Loon had seen in Italy on his personal stylistic development. Unfortunately, virtually no works by his hand from his first Roman period are known. Only van Loon's copy (now in the Église Saint-Jean-Baptiste-au-Béguinage) after a Pietà by the Italian mannerist painter Marco Pino (Basilica di Santa Maria in Aracoeli) is said to have been painted in Rome. Van Loon was greatly influenced by the dramatic light effects and expressive gestures of Caravaggio and his followers such as Orazio Borgianni. He certainly would have seen and studied the former's publicly displayed works, and must have been greatly impressed by his monumental figures and chiaroscuro effects. However, the influence of Dominichino and Caracci is also clear in some works, such as his Assumption of the Virgin (now in the Brussels Royal Museum of Fine Arts, inv. no. 229, see illustration) for which the present work is the preparatory sketch. 

This Assumption was originally painted for and installed in the Saint-Jean-Baptist du Grand Béguinage de Bruxelles, one of the most important beguinages in the Low Countries. The church had been partially demolished under the calvinist regime (1579 - 1585), but was rebuilt; in 1617 the main altar was ready, for which van Loon was to paint the altarpiece, which was finished and installed in 1622. In his career, van Loon painted at least four versions of the Assumption, which was an important theme in the catholic Counter-Reformation, signifying the glory of Mary. The composition of the work is rather traditional: the upper part of the painting is occupied by the divine, with the Virgin Mary and the angels, while the lower part is reserved for the apostles, three of which have been omitted to make room for three holy women, identified as Saint Dorothy (with the basket of flowers), Mary Magdalene (with the long hair) and a sybil with a turban, much influenced by Dominichino's Sibyl of Cumae, which van Loon probably saw with Scipione Borghese on his second trip to Rome. (These women figures were most probably added so the beguines could better imagine themselves into the scene.) 

The oil sketch, executed fluidly and confidently on paper (a practice favoured by Rubens) differs in several ways from the finished painting. Some of the faces are turned in another direction, while two of the women in the foreground have switched places. Furthermore, the woman identified as Mary Magdalene standing behind the two others and pointing at the Assumption bends over much more deeply, and is clearly copied after Barocci's Madonna del Popolo, which he painted for the Santa Maria delle Pieve in Arezzo. (Which would imply van Loon spent some time in Tuscany, too.) Also, in the sketch there is no sign yet of a turban, which was probably added in the definitive composition on request by the beguines. Interestingly, our painting also presents several pentimenti, most notably in the positioning of Mary Magdalene's right arm, which indicates that van Loon was still searching for the right composition.