Haglund succeeded Stefan Wallin as party chair and Defence Minister in June 2012. In March of 2012, Wallin announced that he would not seek re-election to the position of party chair, prompting a low-key contest for the post. Haglund later defeated sitting Justice Minister Anna-Maija Henriksson in the contest.
Wallin had come under severe criticism from the opposition, particularly the Finns Party, for his decision to spare a Swedish-speaking military base, the Dragsvik division in Tammisaari, at a time when other bases had been slated for closure.
A controversial real estate deal in which Wallin had purchased a flat from the Åbo Academy university foundation for 225,000 euros and sold it back to the foundation for close to 400,000 euros was found to be above suspicion.
Haglund had previously been a Member of the European Parliament since 2009. His election to the party leadership in 2012 made him was the youngest-ever chair of the small Swedish People’s Party, which represents Finland's six-percent Swedish-speaking minority.