[2] Severin made his debut as a substitute in Hearts' 3–1 victory over Dundee United on 6 April 1999, and his first starting appearance came three weeks later in a 4–0 win against Motherwell.
[3][4] Severin started to play regularly for Hearts in the 1999–2000 season, making 28 appearances in all competitions and scoring his first professional goal in a Scottish League Cup match against Queen of the South.
[5] In his first ever continental match, Severin scored Hearts' first goal in their 2–0 UEFA Cup Qualifying victory over Icelandic side ÍBV.
[citation needed] In July 2004, Severin left Hearts on the expiration of his contract, and became Jimmy Calderwood's first signing at Aberdeen.
[19] Scotland manager Craig Brown gave Severin his international debut in a 2002 World Cup qualifier against Latvia in 2001.