Born in Kristianstad, Lantz started playing football with amateur club IFÖ/Bromölla IF.
He helped Helsingborg win the 1998 Svenska Cupen and 1999 Allsvenskan titles and had a trial at English club Chelsea in December 1997, before he moved abroad in the winter 1999.
in Italy, where he had limited playing time, Lantz moved to FC Hansa Rostock in the Bundesliga championship in November 1999.
He was instantly a part of the Rostock first team line-up, and in his six seasons with the club, he played 164 league matches.
While at Rostock, Lantz chose to play no longer for the Sweden national team.