The 36-year-old, who came through the ranks of the Blades academy and played 287 games for them between 2000 and 2007, returns to South Yorkshire following a decade-plus of service with the Toffees in the Premier League, signing on 12 years to the day that he previously left..
Jagielka, a former England international who was a member of the Three Lions' 2012 European Championship and 2014 World Cup squads, becomes the Blades' third signing since they secured their return to the Premier League last season, following Christopher Farrugia and Luke Freeman.
Speaking to the club's official website, manager Chris Wilder expressed his delight at securing a homecoming for the veteran centre-back, adding that he feels he will bring a wealth of experience to the dressing room as the club look to establish themselves as top flight mainstays.
"I don't have to sign players for the fans to pat us on the back, we're signing Phil because he is a really good footballer and a great character to have around in our first season back in the Premier League," he stated.
"He's got an obvious history with the club which is fantastic but meeting up with him and seeing his desire makes me delighted to see Jags back at home.
"He's had a fantastic career, he was deserving of his move when we dropped out of the top-flight last time and he went to a fantastic club and played all those games in the Premier League and captained England.
"To have Phil in and around our changing room in one of the most important seasons in our recent history is going to be invaluable.
"He's come to play, he knows he's got to earn his place, but I'm buzzing having spent time with him and seen the desire he's got to succeed at the back end of his career."
The Blades kick off their pre-season schedule in earnest later this month when they face Real Betis before games against Burton Albion, Northampton, Chesterfield and Barnsley ahead of their opening Premier League trip away to Bournemouth.