The 31-year-old defender, who has captained Burton across three divisions, played a major part in the club's successive promotions and Championship survival.
Mousinho made 32 league appearances last season and expressed his desire to secure a new deal, which has now been formally agreed.
He told the official club site: "First of all it was very pleasing to keep the club in the Championship and a great achievement for all the boys but once that happened the priority for me was to sign again.
"I'm massively happy as I have said along that is what I wanted and when the manager called me into his office and said he wanted me to stay it was an easy decision.
"The manager will be looking to add players to the squad here and there but I'm sure if we can keep the base of the team that has done so well we will be set up nicely for next season.
"The Championship was a bit of an unknown for me and you never know how you are going to adjust and adapt. Now I feel in a lot better place with that season under my belt and that experience to call upon."
Mousinho was one of eight out-of-contract first-team players at the end of the season to be offered new deals, with Shaun Barker and Lloyd Dyer having also committed their futures to the Pirelli Stadium outfit.