Courtney Vacher's side will battle it out with their south coast counterparts at the Armco Arena in Solihull, with kick-off scheduled for 11.30am (BST).
Newcastle's reserve side, like the first team, have been in fine form this season and along with Sunday's showpiece, Vacher's side have also reached the final of the Bluefin Sports Insurance Women's Cup.
But with focus fully on the upcoming clash with Pompey, Vacher says the final is a fitting reward for the hard work the young Magpies have put in this term.
"I am absolutely thrilled that the team has reached the FAWNL Reserve Plate final, especially with it being the first season for this group of players in our development team and the monumental effort they've given to get there," she told nufc.co.uk.
"We've done well so far this season, competing well on three fronts, and that is a testament to the togetherness, attitude and application the players show week in, week out, both in training and in the competitive environment."
The development side's captain, Georgina Spraggon, is also looking forward to the occasion. She hopes success in the competition can provide a springboard for further celebrations this term.
"It's a huge opportunity to play at a stadium and also get some silverware, which could be a catalyst to more this season," she said. "We know Portsmouth will be a huge test but we aim to approach the game like we do every other.
"The girls are all very close and are looking forward to training this week, where we will focus on fine-tuning our game so we are in the best possible position for the weekend."
Fellow young Magpie and another influential member of Vacher's dressing room, Jasmin McQuade, reiterated Spraggon's sentiments.
She said: "The opportunity is massive for these girls, especially for some - including myself - who haven't been a part of a final before.
"Each and every one of these girls has grafted all season to earn this place. We have played every single one of the games leading up to this with Sunday in sight.
"With all the support from staff and training we've had leading up to this, we are ready to go out there on Sunday and win."
Members of Vacher's development side ultimately have aspirations to feature for the women's first team in the coming seasons.
And first-team boss Becky Langley believes that reaching two finals in their first full campaign as a group is a good indicator of the young Magpies' upward trajectory.
"It's absolutely fantastic that the development team have got into two finals this season in their first season together," she said.
"It's really important that they get that experience to make sure they're really ready to kick on with the first team. It's brilliant to see them get that experience and game time so they're ready to step up into women's football."
Photograph courtesy of Colin Lock/@Tyneside_NUWFC
