A goal from Dexter Blackstock was enough to secure three points for the Reds, who put themselves in touch with the promotion race following this win over the leaders.
The only disappointment for the home side will be that they had not established a more significant lead, after dominating for long periods - leaving them having to defend desperately in the final stages.
But this was still a landmark win for the Reds, who had begun the season slowly before their recent run of form.
There was something close to a full house at the City Ground and the intense atmosphere was reflected with a frenetic start to the action on the pitch.
With three minutes gone United skipper Alan Smith had already been booked after failing to retreat from a free-kick he had conceded and Steve Harper had been forced into an outstanding save to deny Forest the lead.
That came as Blackstock rose to flick an instinctive header towards the far post after a huge punt upfield from Wes Morgan, with the keeper at full stretch to palm away.
Polish midfielder Radoslaw Majewski also tested Harper, bending a left-footed shot towards the top corner, although the Newcastle keeper was well placed to save.
Forest continued to crank up the pressure, however, and Harper had the woodwork to thank when a second Blackstock header, from a Majewski corner, thumped back off the foot of the post and away to safety.
A flowing move then saw Blackstock and Nathan Tyson combine to tee-up Majewski a shot on the edge of the box which took a deflection as it looped narrowly over.
It took Newcastle almost 25 minutes to register a meaningful effort on goal but when it came they almost took the lead as Ryan Taylor planted a header of his own against the post.
But Forest continued to turn the screw, with Tyson flashing a volley wide, Paul Anderson forcing another strong save from Harper with a powerful drive and Blackstock narrowly off target with a header.
The striker made no mistake on the stroke of half-time, however, as he latched onto Makewski's incisive pass to burst through the centre to slot a simple finish beyond the advancing keeper.
It took a fine tackle from Kelvin Wilson to deny Marlon Harewood an almost certain goal as the former Forest man turned on the edge of the six-yard box as Newcastle began the second half in lively fashion.
Forest had to ride out a long spell of pressure from Newcastle, producing some heroic defending to deny the visitors a clear-cut opportunity.
Kevin Nolan planted one header wide of the target when he might have done better.
But Reds substitute Lewis McGugan also came close with shot from distance that fizzed inches wide.