Mauricio Pellegrino's side had failed to score in their previous two home games but, after Isaac Hayden scored his first Premier League goal in the first half, Gabbiadini equalised early in the second.
The Italian's strike was quickly rendered meaningless when Ayoze Perez scored his first goal of the season, but Shane Long won a 75th minute penalty that Gabbiadini emphatically converted to earn Southampton a much-needed point following back-to-back defeats.
Despite scoring at home for first time since August 19, Southampton's attack still lacked potency, while Rafael Benitez's Newcastle, who sit two points and one place above Saints in ninth, played with far more urgency in the final third.
Pellegrino won two league titles as a player at Valencia under Rafael Benitez and he needs to inject Southampton with some of Newcastle's attacking flair if he is to improve his side's form at St Mary's, where the Saints have picked up just five points in five games this season.
Despite being denied victory on an afternoon when they played the better football, Benitez's men can reflect on a run of three wins and just one defeat in their last six league games as they prepare to face bottom club Crystal Palace at St James' Park next week.
Newcastle had the first sight of goal when Christian Atsu's edge-of-the-box effort hit the side netting, while the best Saints mustered was a 20-yard effort from Dusan Tadic that cleared the crossbar in the 14th minute.
Tadic should have made it 1-0 two minutes later when Nathan Redmond's cross afforded him a free-header at the far post, but his effort looped tamely over the bar.
That miss proved costly as Newcastle went in front after 20 minutes.
Virgil van Dijk, playing his first home game since the protracted transfer saga that almost saw him join Liverpool, made a hash of a clearance and Atsu slammed the ensuing cross against Maya Yoshida before Hayden pounced on the rebound and drilled into the bottom-left corner from the edge of the box.
Van Dijk went close to making amends for his error two minutes later when he outjumped Rob Elliot and headed Redmond's corner just wide from the edge of the six-yard box.
Newcastle hit the crossbar inside the opening minute of the second half when Perez's cross was flicked on by Joselu, and Jonjo Shelvey then drew a good save from Fraser Forster with a shot headed for the top corner of the net.
The home supporters then saw their team score at St Mary's for the first time in almost two months when Gabbiadini turned Javier Manquillo and hooked his foot around the ball to score at the near post from 15 yards out.
But 87 seconds later Newcastle restored their lead when Matt Ritchie broke down the right flank and threaded a pass to Perez, who buried the rebound into the far corner of the net after Forster parried his first attempt.
DeAndre Yedlin was fortunate to stay on the pitch after he slid in two-footed on Redmond, but Newcastle's afternoon was spoiled 20 minutes later.
Florian Lejeune brought down Long as he advanced into the box and the referee awarded the penalty, which Gabbiadini hammered into the top right corner of the net with his left foot.
Lejeune almost made amends in the dying moments of the game when he crashed a header towards goal from a corner but Steven Davis was there to clear the danger and ensure Southampton a share of the points.
Key Opta stats:
- Southampton have only lost one of their last 24 home league matches against Newcastle (W16 D7).
- Perez ended a run of 1135 minutes without a Premier League goal – his last goal came against Bournemouth in March 2016.
- Manolo Gabbiadini scored twice in this match – more than he’d managed in his previous 15 Premier League appearances (1).
- Hayden’s strike was Newcastle’s first in the first half of an away Premier League game since Papiss Cisse scored against Crystal Palace in November 2015.
- No side has been awarded more Premier League penalties in 2017 than Southampton (7, level with Bournemouth).
- This was the first time since the opening day of last season that Southampton recovered from behind at half-time in a Premier League game to earn a point (1-1 vs Watford).