Dolan moved to Franklin’s Gardens as injury dispensation in December, but didn’t play a first-team game.
However, the Saints coaches have been impressed by what they have seen and have opted to keep the 24-year-old on.
He will be viewed as the long-term replacement for South African No.8 GJ van Velze, who is leaving to join Worcester Warriors this summer.
Fa’atoina Autagavaia is also set to depart, with the Samoan utility back heading to France ahead of the new campaign.
Paul Diggin has retired and will continue to coach the next generation of Saints, but Ryan Glynn (Jersey), Tom Warren (Moseley), Sam Harry, Harry Morley and Harry Betts are moving on.
“We have said time and again that success this year has been a squad effort,” said Saints boss Jim Mallinder.
“That includes not only those players that represent the first team, but the entire squad.
“Whether it is playing for the Wanderers, Academy sides, in training or off the field and around the club, every player has made a contribution this season.
“On behalf of the rest of the coaching team I’d like to thank the players who are leaving for what they’ve done in their time at the Saints, and wish them the best for the future.”