The club captain pulled off yet another miraculous goal after coming off the bench to make the difference after Luke Young leveled from Russell Martin's first half opener.
Russell Martin had put the Canaries into the lead after 15 minutes when he capitalized on a scramble at a corner, but Luke Young leveled it on the hour, putting away the rebound when Jamie Mackie hit the post.
But, just minutes after being introduced, Holt first had an effort cleared off the line before putting away a cool finish on 73 minutes which proved decisive, the Canaries getting back on track having failed to win in their previous four games.
Paul Lambert rang the changes in an effort to arrest a slump in results, bringing Simeon Jackson, Andrew Surman and Ritchie de Laet into the starting line-up in an attacking 4-4-2 formation. Neil Warnock, with Joey Barton suspended, also had to contend without goalkeeper Paddy Kenny, who pulled out due to injury, Radek Cerny taking his place between the sticks.
Steve Morison should have put Norwich ahead in the opening minutes. Tussling competitively with Danny Gabbidon as he chased the ball, the Welshman did well to break free and bear down one-on-one, but he let Cerny get too close and dribbled a nonthreatening shot into his waiting arms.
Morison again went close to extending the home side's lead. He first tried a volley on the turn with his right foot which was closed down by a QPR defender, but then just a minute later he found himself in more space and attempted it again, this time his effort fizzing just over the top left corner.
After the half-hour mark the hosts’ superiority began to dim, though Warnock’s men could not find a genuine opportunity to capitalize.
Just before halftime, the chance to get back into it finally arrived for QPR. Shaun Wright-Phillips finally delivered with an excellent probing free kick from the left flank which bounced awkwardly near the far post, but Shaun Derry fluffed the chance and rightly hung his head.
Moments later, Wright-Phillips threatened once more, embarking on a mazy run into the area and forcing Ruddy to parry his shot. The onrushing Mackie reached the rebound but only had enough space to hit the side netting.
The match resumed after the break in a continuation of the quiet affair that characterized the latter stages of the first period, until, on the hour, Mackie drove forward centrally and unleashed a rasping shot that beat Ruddy and came back off the post, finding Young, who needed only to pass the ball into the net.
QPR had all the momentum and Lambert gambled by playing his hand early and introducing Holt and Wes Hoolahan with 20 minutes to go, his final substitutions.
It paid off immediately, with Holt first having a headed effort cleared off the line from Morison’s cross, then immediately set up in the aftermath by Hoolahan for a cool six-yard finish.
QPR streamed forward in search of another equalizer but saw an attempted cross bounce just on top of the far post before the disappointing Alejandro Faurlin wasted a promising position by shooting high over the bar.