Jansson's music career began when he formed a rock band, The Poets, with some of his friends in 2001. That same year, they were chosen to compete in Melodifestivalen with the song "What Difference Does It Make," but did not make it to the finals.

In 2003 Jansson was a contestant in the reality show Fame Factory on TV3 in Sweden. Though he did not win, his first single, "Godmorgon världen," released in 2004, reached #1 on the Swedish charts. His follow-up single "Som sommaren" peaked at #4, but Jansson's third single, "Flickan från det blå," both from his debut album Flickan från det blå, only reached #40.

In 2005, he competed in Melodifestivalen again, this time as a solo artist. He reached the finals with the song "Vi kan gunga," ultimately placing sixth. When the song was released as a single that same year, it received Jansson's highest chart placing, reaching the #1 spot. In the wake of the single's success, Jansson released his second album, Som en blixt, and, several months later, a second single from the album, "En underbar refräng.".

On February 10, 2007 Jansson competed in Melodifestivalen for the third time, singing the song "Amanda" He placed on a shared 3d place in the semifinal and got a place in the second chance round.

On March 3, 2007 Jansson lost the first voting against Sanna Nielsen in the Second chance round of eliminations, meaning that he lost his chance of going to the Eurovision Song Contest.

When "Amanda" was released as a single, it peaked at #2. The album that followed it, Sån e jag, reached #9 on the charts and its second single, "Överallt," peaked at #2 as well, though it only spent two weeks in the charts as opposed to "Amanda"'s twelve weeks.[