The 33-year-old completed the formalities on his deal at Deepdale on Thursday before taking part in training with his new team mates ahead of the weekend’s league opener against Colchester United.
Simonsen has agreed a stay until the end of the season and returns to League One following his departure from Bramall Lane in the summer.
He made 54 appearances for the Blades in 2011/12, ending the season in the Play-Off final at Wembley and will be hoping to have benefited from that experience for his time at Deepdale.
Manager Graham Westley said: “It has been a long summer looking for a goalkeeper after Richard Wright departed the Club.
“During the summer we have seen a lot of goalkeepers and a number of good lads, but Steve fits the bill in all regards.
“I wanted an experienced goalkeeper, somebody who knows the game but still has the enthusiasm and the energy to make a contribution going forward.
“He has got a lot of class about him and a lot of experience, he is a good lad and I am looking forward to working with him."
Simonsen has been handed the number 23 shirt and will be available for selection for the clash with John Ward’s U’s at the weekend.