At the age of twelve he was inspired by The Shadows to start his own instrumental band called Beatboys, where he played rhythm guitar A huge fan of The Beatles he later joined the band Misfits in 1964, where he was a member until co-founding the band Happie in 1967. Writing many of his own songs he was clearly inspired by The Beatles, vocal harmonies and the psychedelia of the time. At 18 he had his first TV appearance with Happie and their song Flowergirl.
Spantell looked set on retiring from music life, and educated himself as a cook in 1969. However he would continue as a musician, mainly as the lead singer of the dance band Kjell Karlsens Orkester. In 1973 he was given the song Kjendis-party, a Norwegian translation of the Ricky Nelson-hit Garden Party. The song became widely popular and reached #4 on Norsktoppen (an official chart for music in Norwegian). His first recording for the Talent label En helt alminnelig sang om sommer reached the #1 spot in 1975.
Through the 1970s Spantell recorded numerous singles and two albums as a solo artist, but most notably he appeared on several albums together with other artists. From 1975 to 1978 he became a part of the enormously popular Treff-gang, a group of four singers (the others being Inger Lise Rypdal, Stein Ingebrigtsen and Gro Anita Schønn) who put out several albums with covers of international hit songs, often translated to Norwegian (during this period the four released nine albums). He toured extensively through the decade, often as part of the Treff-concept, and participated four times in the Norwegian finals for the Eurovision Song Contest. For a period he was also lead singer in another dance band, Torry Enghs.
In 1978 he had a gig in the small fishing community of Båtsfjord in Northern Norway when a fight broke out. Spantell stepped in to separate the fighters and was dealt a serious blow to the throat that crushed his larynx. His singing career seemed over, but he forced himself to participate on the song Sol with the band Strikk, which became a huge radio hit in the summer of 1980.
Spantell then left the music industry and opened up a convenience store. In 1989 he made a brief stint singing in a band performing at the Royal Palace in Oslo, for the 18th birthday of Princess Märtha Louise. He then became the manager for two popular restaurants in Tønsberg and Risør, co-owned by three other artists. From 1996 to 2002 he was cruise manager for the ferry between Bergen, Norway and Newcastle, England before returning to the music business.
In 2004 the up and coming Norwegian rappers Jaa9 and OnklP contacted him about doing a new version of his 1973-hit Kjendis-party. The song became the national breakthrough for the young rappers and one of the most played songs of 2004. Spantell himself made several concert appearances with the boys and its success laid the foundation for a comeback on the Norwegian music scene.
In 2005 he released his first solo album since the 1970s, Det beste fra Dag Spantell, a greatest hits collection including 22 of his songs from 1968 to 1970. Spantell was back performing, and as he himself put it in a 2004-interview: "Now I want to end my life singing."
Dag became a TREFF family member