Jens is son of the well-known Swedish jazz pianist Jan Johansson and brother of the heavy metal drummer Anders Johansson. Highly influenced by classic Rock keyboardists like Don Airey, Eddie Jobson and Jon Lord. In 1982, the classically trained Johansson left the jazz fusion band Slem and joined the Swedish metal band Silver Mountain, which also included Anders. In 1983 he left Sweden for California and joined guitarist Yngwie Malmsteen as a member of his band, Rising Force. Numerous records and world tours ensued and he stayed with Yngwie until 1989. Jens also played with the band Dio between 1989 and 1990. Like Anders, he began an ongoing collaboration with Jonas Hellborg in 1989 which has resulted in several well-received progressive and avant-garde recordings, including Dissident, Silent Run (an acoustic piano trio record with Ginger Baker on drums) and the hard core progressive fusion record, E.
In 1993, Jens co-founded a progressive blues metal project, The Johansson Brothers, and recorded a self-titled record. In 1996, with a different line-up, they recorded another album, Sonic Winter, this time under the name Johansson with Yngwie Malmsteen guesting on guitar. The last Jens record, The Last Viking, a more 'European metal' oriented album, was released in 1999 with special guests Michael Romeo and Göran Edman.
Jens has released several instrumental solo records such as Fjäderlösa Tvåfotingar, Ten Seasons (a piano solo album improvised in the Mark Kostabi gallery, New York), Heavy Machinery (with Anders and Allan Holdsworth) and Fission (with Anders, Shawn Lane and Mike Stern) and many collaborations with other artists, metal compilations and Berends Brothers' band Mastermind.
He co-founded Heptagon Records to distribute his own recordings and that of other musicians, such as guitarist Benny Jansson and bassist Magnus Rosén.
Since 1995 he has been a member of Power metal/Neo-classical metal band Stratovarius, and he is still releasing solo albums and appearing as a guest or session musician in other projects.