A member of the Royal Swedish Academy of Sciences since 1994, Janson has been the chaired professor of mathematics at Uppsala University since 1987.
After his 1968 matriculation at Uppsala University at age 13,[6] Janson obtained the following degrees in mathematics: a "candidate of philosophy" (roughly an "honours" B.S.
Janson's ongoing research earned him another PhD from Uppsala University in 1984 – this second doctoral degree being in mathematical statistics;[10] the supervisor was Carl-Gustav Esseen.
Janson's former doctoral student, Ola Hössjer, received the Göran Gustafsson prize in 2009, becoming the first statistician so honored.
[13] In December 2009, Janson received the Eva & Lars Gårding prize from the Royal Physiographic Society in Lund.