He wrote under the pseudonym Vitalis (which roughly means "life is a battle" in Latin).
Although he grew up in poor circumstances he studied at Uppsala University and got a Master of Arts degree.
His poetry was characterized by the ideals of romanticism, i.e. melancholy and spiritual ecstasy, but he also wrote many comical and satirical poems.
Among his most widely known poems are Enslingens sång i den stora öknen ("The lonely man's song in the great desert") and Komiska fantasier ("Comical fantasies").
Sjöberg made translations of Thomas Moore and Washington Irving.