Lasse Johnson's ability to draw became apparent at an early age and his family began to recognise his talent at the age of 13. However, there were no educational opportunities in the small village outside Värmland where Johnson grew up. Instead, he moved down to Malmö to attend the 'Figure and Landscape Drawing' course at the Hermods korrespondentinstitut. In 1918, he bought a one-way ticket to Stockholm and enrolled at the Althins målarskola. In 1920 he was accepted to Konsthögskolan in Stockholm and studied there until 1924. In his first year at Konsthögskolan, Johnson had the opportunity to exhibit in Örebro, where the recessions were mixed: 'Lasse Johnson is a colourist and is such a pronounced contrast to his peers that in a couple of canvases he even approaches Cubism. However, he wisely stops before art turns into weirdness and is content to present things that are enjoyable even for ordinary mortals" (Extract from Nerkes Allehanda 1920).
In 1922 Johnson exhibited at the Vårsalongen at Liljevalchs. Despite the many exhibitors and paintings, he stood out to the mainstream art critics. The breakthrough was a fact and Johnson had solo exhibitions in Oslo in 1924, at Lilla utställningen in Stockholm in 1926, at Gummesons konsthall in 1930, Konstnärshuset in Stockholm in 1933, 1936, 1940 and 1943, at Värmlands museum in 1936 and 1954, and a retrospective exhibition at Konstakademin in 1948.