Berger, has signed a two-year deal at Fratton Park.
"Myself, Milan and Harry have worked extremely hard to make this happen," Pompey's chief executive Peter Storrie told the club's official website.
"A lot of big clubs were interested in Patrik and we have persuaded him to sign for Pompey where he can see the potential of what we are trying to do at Fratton Park.
"We think this speaks loud volumes for the progress of Portsmouth Football Club."