Joe Kinnear's struggling side had looked to be heading for another damaging home defeat in the Premier League.
The visitors had hit back after Michael Owen had opened the scoring early in the game with goals from former Magpie Craig Bellamy and Carlton Cole.
But Gateshead-born Carroll - just four days after his 20th birthday and on his first competitive home start - rose above the visiting defence 12 minutes from time to head a Damien Duff cross past Robert Green and level the scores at 2-2.
The result lifted Newcastle above Manchester City and Portsmouth and into 12th place, while West Ham remain 10th in the table.
Owen had struck the post early in the game after latching on to a pull back from Jonas Gutierrez, but he made no mistake six minutes later.
He took a ball from Jose Enrique 25 yards from goal and strode forward to the edge of the box before beating Green at his near post for his 10th goal of the campaign.
Carroll headed inches wide in the 26th minute after Danny Guthrie cross from the right and United were made to pay for that miss three minutes later by Bellamy.
The striker - whose every touch was booed by Newcastle's fans - played a one-two with another United old boy, Scott Parker, before skipping into the box and lifting the ball over Shay Given.
It was Bellamy's 100th career league goal and with a large proportion of those strikes having come during a colourful few years on Tyneside, it was probably fitting that he passed the milestone at St James' Park where he was once feted, and not booed, by Newcastle's loyal fans.
Given had to be at his best to deny Mark Noble before the half was up, stopping his low shot with his legs, and Bellamy struck the loose ball into the side-netting.
Cole, however, was bang on target 10 minutes after the break when a lofted ball forward from Herita Illunga dropped at his feet in the box, with his shot leaving Given with no chance.
Kinnear threw on Charles N'Zogbia for the last half hour and the midfielder, who this week claimed his agents were in talks with Tottenham Hotspur and Aston Villa, was booed on to the pitch, while Geremi, who made way, was also given short shrift by the home fans.
Visiting defender Lucas Neill had the ball in his own net in the 68th minute when he badly sliced an attempted clearance, but it was ruled out by referee Alan Wiley for a push in the box by Steven Taylor.
Just as United's fans were losing hope, Carroll was there to head a Duff cross home and in doing so limit the damage for Kinnear's side, who had badly needed all three points to kick-start their faltering league campaign.