Poynting was born at Monton, near Manchester, and educated at the universities of Manchester and Cambridge (1872–76). He served as professor of physics at Mason Science College (later the University of Birmingham) from 1880 until his death in 1914.

He wrote on electrical phenomena and radiation and is best known for Poynting's vector, introduced in his paper On the Transfer of Energy in the Electromagnetic Field (1884). In this he showed that the flow of energy at a point can be expressed by a simple formula in terms of the electric and magnetic forces at that point.

In 1891 he determined the mean density of the Earth and made a determination of the gravitational constant in 1893 through the accurate use of torsion balances. His results were published in The Mean Density of the Earth (1894) and The Earth; Its Shape, Size, Weight and Spin (1913). Poynting was also the first to suggest, in 1903, the existence of the effect of radiation from the Sun that causes smaller particles in orbit about the Sun to spiral close and eventually plunge in. This was developed by the American physicist Howard Robertson and was related to the theory of relativity in 1937, becoming known as the Poynting–Robertson effect.