Member of the Royal Netherlands Academy of Arts and Sciences Johannes van Laar (10 July 1860 – 9 December 1938) was a Dutch chemist who is best known for the equations regarding chemical activity (Van Laar equation).

Van Laar's parents died when he was still a minor, his mother in 1862 when he was about 2-years-old and his father in 1873 when he was about 13-years-old.

After several trips on steam ships and reaching the rank of a sub-lieutenant he asked for discharge when he became of age.

Van Laar started his studies of physics, chemistry and mathematics at the University of Amsterdam in 1891.

After being a teacher at a middle school he became unsalaried lecturer at the University of Amsterdam 1898 and assistant of Bakhuis Roozeboom in 1902.