Schmitz studied medicine in Groningen (1639), Leiden (1643), and Angers.
He became Professor of Medicine (1648) and rector (1650) of the University of Harderwijk.
He married Gertrud Kumpsthoff and had a son Johann Dietrich Schmitz (1648/1649-1692), who became mayor of Cleves, and a daughter Sophia (c. 1644-1671).
Schmitz is known for his posthumous work Medicinae practicae compendium (Harderwijk 1653, Copenhagen 1659, Paris 1666, Utrecht 1682, Leiden 1688).
Georgius Hornius' preface to this work mentions the deceased author's never-realized plan to publish a botanical work, Plantarum Velavicarum Historia.