McFadzean, 27, completed a medical and agreed personal terms with the Club on Thursday before putting pen-to-paper on a two-year deal with an option, which will keep him at stadiummk until at least June 2016.
The colossal centre-back joins the Dons after spending the past four seasons with Crawley, where he made a total of 155 appearances and helped the Red Devils win promotion to both League 2 and League 1.
He becomes Karl Robinson’s third signing of the summer after winger Danny Green and midfielder Mark Randall.
Speaking to MK Dons Player after finalising his move, McFadzean said: “I can’t wait to get started. I’ve known (of MK Dons’ interest) for a couple of weeks and I’m delighted to finally get it sorted.
“The Gaffer wants to go where I want to go and I also know Richie Barker from before. The style of football the team plays will suit me. The manager has already told me what he wants from me here and it’s what I want to.
He continued: “I wanted a new challenge, and if you look around the place it’s a big challenge but one I’m looking forward to. I’m sure coming here will improve me as a player too.
“I just can’t wait to put the shirt on and kick a ball about in this wonderful ground.”
Born in South Yorkshire, McFadzean began his career as member of the Sheffield United Academy.
At the beginning of the 2005/06 season, he was given a squad number at Bramall Lane and went on to make his debut that year as a substitute in a League Cup tie against Shrewsbury Town.
In July 2007, McFadzean moved to non-League outfit Alfreton Town where he helped the Reds reach the Conference play-offs in two of his three seasons at North Street.
The defender’s performances in Alfreton colours earned him a call-up to the England C team and then, in August 2010, a move to Crawley for what was reported to be a substantial fee.
Quickly establishing himself as first-choice centre-back at the Checkatrade Stadium, McFadzean was named in the Conference Team of the Year in 2011 while also helping the Red Devils earn promotion to the Football League.
The 6ft 1in stopper’s strong showings continued and the following season he was named in the PFA Team of the Year due to his stand-out role in Crawley’s promotion to League 1.
McFadzean, who became Crawley’s longest-serving player during his time in Sussex, featured 46 times last season, missing just four League fixtures including the Dons’ 2-0 victory on Boxing Day.
Stay tuned to mkdons.com for further reaction to the McFadzean signing.