Mousinho left Stevenage to be reunited with former boss Graham Westley on a two-year contract on Tuesday, becoming the 11th signing of a radical summer overhaul at Deepdale.
"It is a really exciting time for the club and for myself," the 26-year-old told North End's official website. "I have worked with the manager for the last couple of years and he played a big part in whether I was going to sign for the club.
"The club itself plus the supporters and the history made it an easy decision in the end and I am excited about the future.
"I have been following all the signings and more enthusiasm is building around the place ahead of the new season. We are signing good accomplished players with proven track records and backgrounds.
"We have signed club captains and players of the year. Everybody at the club is hopeful about what is to come."