Jazz Younger has put pen to paper on a new contract, subject to FA approval.
The defender's new deal is one-year long, with a club option of an additional 12 months.
The 22-year-old joined Pompey in July 2018 following her departure from Brighton & Hove Albion.
And Younger becomes the club's longest-serving player, with her stay now totalling five years.
The current holder of the Player of the Season trophy has since gone on to make 96 appearances and has scored 10 goals.
And she struck half of that amount during the 2022/23 season, notably netting a last-gasp winner at Billericay and an audacious flick against Plymouth earlier this year.
Blues boss Jay Sadler said: "This deal is great news for the club. Although joining five years ago, it has been within the past few seasons where Jazz has proved to be such a vital part of our squad.
"She possesses all the qualities you would want in a central defender, both with and against the ball, and yet we still believe there’s so much more to come.
"Her impact in both boxes is just as influential as it is in the dressing room. Jazz will continue to be a big part of our drive to bring success to this club over many years to come."