Olsson, like his brother, is a full Sweden international and is also left sided, although he can also play up front.
Now the 23-year-old has told the Swedish press that he has completed a move to Blackburn after his contract with Halmstads expired.
"It feels great, I tried not to think about it too much before it was confirmed, but I signed today and can finally take a breather," Olsson told Hallandsposten.
His agent claims he rejected a move to Italy to join Rovers.
"Two clubs in Serie A and Standard Liege wanted him, but for Marcus it was a dream to play in the Premier League and even more so with his brother," Hasan Cetinkaya told Aftonbladet.