The 27-year-old has penned a two-year contract after being released by Preston.
The versatile former Rangers trainee scored twice in 18 appearances for the Npower League One club, but played only once after Graham Westley was appointed manager in January.
McLean said: "I want to help the squad replicate and improve what they have achieved here in the last few years. I will look forward to the European games but it really is a privilege to join this fantastic club. Opportunities like this do not come along too often."