In his early teens, a relative lent him records of Miles Davis, Ben Webster, and Mose Allison. During the 1960s, he followed the fashion and developed an interest in the organization He listened to Kjell Öhman play with the Telstars, to Jimmy Smith and Jack McDuff, and to Hammond organ music
Drummer Sjunne Ferger became an important figure in his life, and together they formed a duo: "Takt & Ton" (Beat & Pitch).
In 1970, after graduation from upper secondary school, he took a semester off, planning to go on and study medicine. He ended up at dental school, but after a year and a half he decided to switch to music
He was accepted at the Göteborg College of Music, where all the professional musicians had their jam sessions at night. That gave him the opportunity to play with Ove Johansson, January Forslund, Conny Sjökvist, Gilbert Holmström, Gunnar Lindgren, and others, and he discovered Herbie Hancock, McCoy Tyner, Paul Bley, Bill Evans, Lennie Tristano, Keith Jarrett, and Chick Corea.
He also played with the Arild Andersen Quartet.
He went on to play with Radka Toneff and various Norwegian musicians, including Knut Riisnaes and January Garbarek, and then with Hawk On Flight, Equinox, Red Mitchell, Joakim Milder, Crystal Eagle, and many other groups, both Swedish and Danish. Today, the Lars Jansson trio is, and has long been, one of the most well-renowned jazz groups in Sweden. Originally, the other two members were Anders Jormin and Anders Kjellberg.
Lars Danielsson succeeded Jormin as the trio"s bass player in the mid-1980s, and since January 2005 he has been succeeded by Christian Spering.
Lars became a member of Björn Alke"s quartet, with Gunnar Bergsten.