The Finnish Swede Haldin made his world championship debut in 1999 with a 27th place on the long distance in Scotland. The long distance should become his home route: at all European and World Championships, he started on this route. This was also the case in 2001 at the World Championships in Tampere , when he finished ninth in the top ten in the world. In the same year he was also 12th in the middle distance race in the context of the World Games taking place in Japan . A country distance race was not held.
In 2002 he won the multi-day O-ring competition in Sweden. The following year he succeeded in defending his title in this competition. In September 2002 he started at the European Championships in Sümeg, Hungary . On the long distance he reached fourth place, while he won the season for Finland together with Jani Lakanen and Pasi Ikonen . In the overall World Cup, he finished the season third behind the Norwegian Bjørnar Valstad and the Russian Michail Mamlejew . In 2003 in Switzerland he won his first world championship medal. The Finnish relay with Lakanen, Jarkko Huovila and Haldin won silver behind Sweden. In the single start over the long distance, it was only enough for a 16th place.
At the 2004 European Championships in Roskilde , Denmark , he finally won the only medal in an individual decision at international championships in his career. Two days after defending his title with the relay, he was second behind the Swede Kalle Dalin in the long distance race with 14.5 km as the crow flies . As a result, Haldin was able to place well several times at international championships. Six times he was in the top eight at world championships. With the Finnish relay he won three medals in 2006 (silver), 2007 and 2009 (both bronze). In 2008 the Finns also finished third at the European Championships.
Haldin belonged during a career to the clubs IF Femman (until 2001), Halden SK (2002 to 2007 and since 2010) and IFK Göteborg (2008 to 2009). With Halden he won the Jukola season in 2003, 2010 and 2011 and the Tiomila in 2002, 2003, 2004, 2006, 2007 and 2012 . At Finnish championships he won the 2001 relay, 2007 sprint and 2009 ultra long distance titles.
