The goalkeeper was previously at The Crest Finance Stadium prior to joining Baffins ahead of the 2018/19 season.
He was the club’s penalty shoot-out hero when they defeated Bemerton Heath to lift the Russell Cotes Cup in 2016/17.
Scott helped Baffins win the Wessex League Cup in his first season and was an ever present during last season’s Premier Division campaign.
Scott, though, was one of four players released by boss Shaun Wilkinson in the aftermath of Baffins’ 5-0 friendly loss to US Portsmouth last weekend.
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Charlie Searle will be Baffins’ first choice in 2020/21 while Scott will give Brad Snelling new competition at the Royals.
Snelling played all but one of Portchester’s 28 league games last season, with Searle in goal for the one he missed.
Scott joins a lengthy list of summer signings by boss Mick Catlin in a squad which will start the season as firm Wessex Premier title favourites.
Mike Gosney, Craig Harding, Liam Hibberd, Luke Dempsey and Joe Chamberlain have arrived from Alresford, while striker Lee Wort was signed from Sholing and wideman Toby Adekunle, once of AFC Totton, arrived from Sussex non-league football.
Ex-Pompey Academy pair Oscar Johnston and Ethan Robb have also signed, while assistant manager Lee Molyneaux has been playing in friendlies.
Portchester’s latest friendly is at home to Cribbs this Saturday (3pm). The Bristolians are managed by Richard Luffman, who was in charge at Alresford last season and whose summer departure from Arlebury Park was followed by most of his squad.