Tuomas Haapanen studied the violin at the Sibelius-Academy in Helsinki. After his debut in 1948 he continued his studies in Paris with Léon Nauwinck and René Benedetti.

In addition to a fine career as soloist and chamber musician, he was also concertmaster of the Finnish Radio Symphony Orchestra and the Helsinki Chamber Orchestra.

In 1962 he was appointed head violin teacher at the Turku Conservatory, and in 1978 he became violin professor at the Sibelius-Academy, where, from 1987 to 1990 he also acted as principal. He has held master classes in Europe, USA and Japan, and many of his students have won prizes in international competitions. In 1999 he received the Finnish State Music Prize.

Tuomas Haapanen acted as the chairman of the International Jean Sibelius Violin Competition in 1981-2001, and has regularly been invited to serve as member of the jury in most major violin competitions.