Blackburn now have two Olssons on their books after manager Steve Kean completed the signing of Martin's twin brother Marcus.
Centre-back Martin joined Rovers on transfer deadline day in 2006, and now winger Marcus has followed suit on Tuesday.
Blackburn's website has confirmed Marcus has joined the Ewood Park club on a free transfer from Swedish side Halmstad, signing a two-and-a-half-year deal through to the summer of 2014.
The 23-year-old, who can also play up front, is now awaiting international clearance on the deal from the Swedish FA and FIFA.
The Olsson brothers both started their careers at local side Hogaborgs BK and had a trial with Blackburn at the end of 2005.
However, while Martin signed a contract under then manager Mark Hughes, Marcus returned to Sweden and eventually signing for Halmstad in 2008, scoring 17 goals in 139 appearances.