Austrian astronomer, mathematician, and physicist. He was the first to investigate and catalogue double stars, though his equipment was unable to distinguish true binary stars (in orbit round each other) from separate stars seen together only by the coincidence of Earth's viewpoint.

Mayer was born in Moravia. He became a Jesuit priest and in 1752 professor of mathematics and physics at Heidelberg. When the elector palatine Karl Theodor built an observatory at Schwetzingen, and then a larger one at Mannheim, Mayer was appointed court astronomer. He lost this post with the pope's dissolution of the Jesuit order in 1773, although he managed to continue his astronomical studies.
Mayer measured the degree of the meridian, based on work conducted in Paris and in the Rhineland Palatinate, and observed the transits of Venus in 1761 and 1769. The latter observation was conducted in Russia at the invitation of Catherine II.