Stamitz was born in Nemecky Brod (now Havlickuv Brod, Czech Republic). His first music lessons came from his father, an organist. He later studied at the gymnasium in Jihlava and at Prague University. In 1741 he went to Mannheim, becoming first violinist of the court orchestra there in 1743 and concertmaster in 1745. He raised the level of the orchestra to a point where it was one of the most respected in Europe. In 1754-55 he spent time in Paris, where his music was well received. He died two years later in Mannheim.
Stamitz, generally regarded as the founder and most prominent member of the so-called Mannheim School of composers, wrote a number of concertos (mainly for violin or flute), a quantity of chamber music and a mass (1755). His most significant works, however, are his symphonies, of which he wrote over fifty. He was the first composer to regularly write symphonies in a four-movement form, adding the minuet and trio to the other three standard movements. In introducing a second group of contrasting thematic material to his opening movements, he also did much to develop what would become known as sonata form.
Johann was the father of Carl Stamitz and Anton Stamitz, also composers.