Cartographer and publisher in Amsterdam. Son-in-law of Jodocus Hondius (1563-1612), who had published the Mercator-Hondius Atlas from 1606.
After 1630 Janssonius became partner of his brother-in-law Henricus Hondius (1597 – 1651), who had succeeded his father together with his brother Jodocus Hondius, Junior (1594 – 1629) in 1612. A new edition of the Mercator-Hondius Atlas by J. Janssonius and H. Hondius in 1631 was followed by a second volume in 1633. As 'Atlas Novus' or 'Theatre du Monde' three volumes had been published until 1639. In 1640 H. Hondius retired and Janssonius became publishing director. Under the leadership of Janssonius the 'Atlas Novus' was steadily enlarged to an atlas-work of six volumes, published in Latin, French, German, and Dutch in the following years.
The first three volumes contained maps of Northern and Eastern Europe and of Germany (vol. 1), of the Netherlands, France and Spain (vol. 2) and of Italy, Greece and maps of the continents (vol. 3). The fourth volume, first published in 1646, was fully dedicated to the British Isles, the fifth volume, published in 1650 for the first time, was an atlas with sea charts (Atlas Maritimus) and the sixth volume included maps of the Ancient World.
Until 1662 the atlases published by Janssonius - meanwhile called 'Atlas Major' - increased to eleven volumes, including a Townatlas and the famous Atlas of the Heavens by Andreas Cellarius (volume 11). All in all a monumental work, which contains the work of about a hundred authors and engravers. J. Janssonius' publishing company was continued by members of his family, esp. by his son-in law Johannes van Waesberg (died 1681).