Gerard was born in Tilburg, an older brother of Cornelis van Spaendonck (1756–1840), who was also an accomplished artist.

He contributed over fifty works to Les Vélins du Roi, a famous collection of botanical watercolors possessed by French royalty.

From 1799 to 1801 he published twenty-four plates of Fleurs Dessinees d'apres Nature (Flowers Drawn from Life), which were high-quality engravings for students of floral painting.

Today, Spaendonck's Fleurs Dessinées d'après Nature is a highly treasured book on floral art.

In 1788 he was appointed adviser to the Académie, and in 1795 became a founding member of the Institut de France.