His childhood was fatherless and poverty-stricken, his mother suffered from mental frailties and Lehtonen himself was forced into paupery.
Lehtonen's foster mother supported his schooling.
He was able to study literature for a few years in the University of Helsinki, but dropped out without completing a degree.
As an author, he began as a neoromanticist, but after the Finnish Civil War his outlook transformed into deep pessimism and disenchanted scepticism.
Having suffered for years from various ailments, he committed suicide by hanging himself with a rope, that had been used to wrap up a parcel of books, in November 1934.