Pompey have signed Callum Johnson from fellow League One side Accrington for an undisclosed fee.
The 23-year-old right-back – who has been handed the number two shirt – has penned a two-year deal, with the club holding an option for a further 12 months.
Blues boss Kenny Jackett said: “He’s someone who we’ve been tracking for a while now and we’re delighted to add him to our defensive options.
“Callum is only young, but has already gained a lot of experience over the past few years at Accrington.
"He’s someone who we’ve been tracking for a while now and we’re delighted to add him to our defensive options."
“We do feel that it’s the right time for him to come here and take up the challenge of playing for Pompey.”
Johnson progressed through the academy at Middlesbrough and joined Accrington – initially on loan – in the summer of 2017.
The versatile defender can play anywhere across the back four and has also featured in the centre of midfield.
He made a total of 119 appearances during his time with Stanley, scoring his only goal in a 2018 victory over Forest Green.