The Scottish midfielder arrived at Bramall Lane back in 2016, when he joined from Coventry City. Sheffield United were a League One side when they secured Fleck’s services and he was instrumental as they escaped the third tier in 2017.
Fleck has departed Bramall Lane having made 278 appearances for the Blades in all competitions.
He has joined Blackburn on a free transfer, penning a deal that runs until the end of the season.
A statement issued by Sheffield United read: “Long-serving John Fleck has left the Blades on transfer deadline day. The midfielder – a star of promotions from League One and the Championship – has joined Blackburn Rovers on a permanent deal.
“Fleck, 32, a winner of a number of Player of the Year awards, registered his final Blades appearance in the December encounter with Liverpool. The Scottish international was one of the first signings by Chris Wilder in the summer of 2016 and went on make significant contributions on the journey to the Premier League.
“He made a total of 278 appearances for the Blades, scoring 16 goals in his seven and a half years with the club. Best wishes, Flecky.”