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

In 1769 he moved to Paris, where in 1774 he was appointed miniature painter in the court of Louis XVI.

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.