Ingenhousz, who was born at Breda in the Netherlands, studied medicine, chemistry, and physics at the universities of Louvain and Leiden, receiving his MD from Louvain in 1752. In 1765 he visited London and became expert at administering smallpox inoculations using Edward Jenner's method. News of his expertise spread and he was invited to Vienna in 1768 by the Empress Maria Theresa to inoculate her family and to become court physician.

In 1779, Ingenhousz returned to England and published his work on gaseous exchange in plants. His experiments demonstrated that plants absorb carbon dioxide and give off oxygen (in his words, “purify the air”) only in the light, and that the reverse process occurs in the dark. The light process later became known as photosynthesis. Ingenhousz also conducted research on soils and on plant nutrition, improved apparatus for generating static electricity, and studied heat conduction in metals.