They have been without a permanent manager since they sacked Danny Cowley more than two weeks back following a bad run of form.
Simon Bassey has been in interim charge and Portsmouth have been holding talks with several candidates, with interviews conducted.
It emerged earlier on Thursday that the club are seriously considering giving the job to rookie manager Mousinho.
And it has been claimed that the 36-year-old Oxford United player-coach is set to become the next Portsmouth boss.
Following a process that lasted for over two weeks, the League One club have decided to gamble on Mousinho.
He signed a two-year contract with Oxford United as player-coach in 2021 but is now set to become the next Portsmouth manager.
Former MK Dons boss Liam Manning and England Under-20 coach Ian Foster had second interviews with the club.
However, Portsmouth have taken the call to go with Mousinho as their new permanent manager.
