Mark O'Mahony is joining Reading on a season-long loan, where he will play under fellow Irishman Noel Hunt.
Technical director David Weir said, "The aim with all our young players is for them to play regular senior football, and this loan will give Mark that chance this season.
"He's shown his undoubted potential in the Championship with Portsmouth last season, and during his three appearances for us in the Premier League.
"This move provides him with the platform to get regular games and goals and continue his development."
The Irish under-21 international spent last season with Portsmouth. Injury severely restricted his game time to just 13 appearances during his spell at Fratton Park, but he contributed an impressive return of three crucial goals across less than 600 minutes as Pompey retained their position in the Championship following promotion.
David added, "After a frustrating last season Mark has been with us this previous week and shown he is back to full fitness, raring to go and ready for the new season. We will be following his progress with interest."