Between 2009 and 2012, Evans scored 48 goals for the Blades before he was convicted of rape, which led to the club releasing the Welshman.
However, after spending two-and-a-half years in prison, Evans was found not guilty following a retrial and he subsequently linked up with Chesterfield for the 2016-17 season.
Rumours of a return to Bramall Lane emerged a number of weeks ago, and it has now been confirmed that he has penned a long-term contract at the Yorkshire outfit.
The 28-year-old told the club's official website: "I am delighted to be back. I still feel I have plenty to prove in football both at club and international level and I believe I can achieve those goals at United, playing in front of the terrific fans whose support I have always appreciated.
"I am very grateful to Chesterfield, the board and football management for giving me an opportunity to return to the game. It is just disappointing that it has come in season which has seen the club suffer relegation. I would like to thank the Chesterfield fans who made me feel so welcome."
Evans scored five goals in 25 appearances in League One this season.