At the age of nine, he began taking cello lessons while three years later starting to learn how to play the guitar, today his main instrument.
In addition he worked as a guitarist on tours with artists such as Roxette, Michael Ruff Band, Nils Landgren Funk Unit, Tomas Ledin and Ratata.
[1] Alongside arranging and producing music, Janson also writes songs within different genres, from pop and jazz to classical crossover, often in collaboration with other songwriters.
Songs co-written by Janson include "You're Out of My Life" (Darin), "Don't Tell Me You're Sorry" (S Club 8), "Fools" (Rachel Stevens), "Come Primavera" (Il Divo), "What You Believe In" (Take That), "Like Suicide" (Christian Walz), "The Queen" (Velvet) and "Discoteque" (Elin Lanto).
[1] Through the years, Janson has collaborated with artists such as Aqua, Backstreet Boys, Benny Andersson, Bernard Purdie, Brenda Russell, Britney Spears, Céline Dion, Cody Karey, Eddie Harris, Emilia Mitiku, Il Divo, Katherine Jenkins, Kelly Rowland, Maceo Parker, Max Martin, Michael Bolton, Michael Ruff, Nils Landgren, Paul Potts, Peter Jöback, Pink, Randy Brecker, Robyn, Ronan Keating, Roxette, Take That, the Tenors, Toots Thielemans, Westlife and Arch Enemy.
During the following banquet held at the Stockholm City Hall, the classical crossover composition "Anthem for All Mankind",[11] with music written and produced by Janson for the event, was performed by the Swedish opera trio Divine.