He was born and grew up in Gothenburg, attended secondary school at Hvitfeldtska and early on his interest in music grew from jazz music, through Bob Dylan to a more rock’n’roll oriented sound. He joined Nationalteatern in 1971 as guitar player and soon became the leading member when it came to writing the group's songs, such as "Barn av vår tid" (Children of Our Time) and "Bara om min älskade väntar", a Swedish translation of Bob Dylan's "Tomorrow is a long time". In 1975 Dageby appeared under the pseudonym "Sillstryparn" at the "Alternativfestival - an alternative to the Eurovision song contest - performing "Doin the omoralisk schlagerfestival". He was also one of the main songwriters in the Tältprojektet (The Tent Project), a musical theater performance on the history of the Swedish working class, which toured the country the summer of 1977. Dageby made his debut as a solo artist in 1983 with the album En dag på sjön, in addition to his solo work and the many reunions with Nationalteatern Dageby has written much music for Swedish film and television.