Brewster, who was born in Jedburgh, Scotland, started by studying for the ministry at Edinburgh University but, after completing the course, he abandoned the Church for science. He earned his living by editing various journals and spent much time popularizing science.

Brewster published almost 300 papers, mainly concerning optical measurements. He was an early worker in spectroscopy, obtaining (1832) spectra of gases and of colored glass. His most famous work was on the polarization of light. In 1813 he discovered Brewster's law, which states that if a beam of light is split into a reflected ray and a refracted ray at a glass surface, then they are polarized, and the polarization is complete when the two rays are at right angles. The angle of incidence at which this occurs is called the Brewster angle. He is also known for his invention, in 1816, of the kaleidoscope.

Brewster was knighted in 1832. From 1859 he was principal of Edinburgh University.