The former England manager quit shortly after Forest were beaten 3-1 by Birmingham at the City Ground.
McClaren had only been at the City Ground since June but, in the aftermath of Sunday's defeat, tendered his resignation to chairman Nigel Doughty.
Forest, who lie just one point and one place above the npower Championship relegation zone, have already started the search for McClaren's successor.
McClaren, who was vilified by England fans after he failed to qualify for Euro 2008, was never a popular choice with Forest fans.
His arrival as Billy Davies' replacement over the summer was greeted with scepticism from some supporters, but he was expected to build on the foundations put down by his predecessor.
McClaren encountered the same problems in the transfer market that had annoyed Davies, though, with an apparent lack of backing from the club's board leaving him frustrated.
"I resigned - they don't share the ambition that I came for," said McClaren.
NFFC statement read: "Nottingham Forest can confirm that Steve McClaren has resigned from his role as manager.
"He has left the club without compensation - nor will he be seeking any. The club can confirm that the search for a new manager will begin immediately.
"Mr Doughty has also announced his intention to step down as chairman of the club at the end of the season after 10 years in the role.
"The search for a new chairman will commence immediately."
WOLVES 1 NEWCASTLE UTD 2
WOLVES: Hennessey, Stearman, Johnson, Berra, Ward, Hunt (Guedioura 58), Henry (Hammill 58), O'Hara, Jarvis, Doyle, Fletcher.
Subs Not Used: De Vries, Edwards, Vokes, Zubar, Doherty.
NEWCASTLE: Krul, Simpson, Steven Taylor, Coloccini, Ryan Taylor, Obertan (Marveaux 90), Cabaye (Guthrie 89), Tiote, Gutierrez, Best, Ba (Lovenkrands 71).
Subs Not Used: Elliot, Santon, Ben Arfa, Sammy Ameobi.
Att: 26, 561
Alan Pardew said after the game "we rode our luck, with the help of a few interesting referee decisions", but if one man made the headlines ahead of the ref it was Tim Krul.
Krul produced a man-of-the-match display to move the Magpies up to third in the Premier League with a 2-1 victory over Wolves.
Krul conjured a handful of stunning saves as Wolves slumped to a fourth consecutive defeat, despite Steven Fletcher setting up a frantic finish with a diving header in the 88th minute.
With Krul in magnificent form at one end, it was Demba Ba and Jonas Gutierrez who saw United home at the other to extend their unbeaten top-flight run to 10 games
Inside the first 13 minutes it was evident as to why Newcastle can proudly boast the stingiest defence in the top flight, the Magpies conceding just four goals now in their first seven matches.
With less than two minutes on the clock, Dutchman Krul underlined his growing reputation, in particular as the bedrock of United's back five.
With Jamie O'Hara's 22-yard curling free-kick dipping towards the bottom right-hand corner after evading a number of heads, an alert Krul averted the danger with a full-stretch save.
Eleven minutes later Krul showed remarkable versatility, and kept his wits about him as he used his face to block an attempted lob from Kevin Doyle on the edge of the area after the striker had been played in by a knock-on to a goal-kick from Wayne Hennessey.
But for those two saves the outcome could have been very different as the visitors had showed no threat in the opening exchanges.
After Gutierrez then stroked a low, right-foot curler a couple of yards wide in the 14th minute, three minutes later Ba caught Wolves defence, and goalkeeper Hennessey, fast asleep.
From a Yohan Cabaye corner looped into the near post, nobody picked up Ba's run, and as Hennessey came to collect, the striker stole in for a simple nod down from two yards for his fourth goal in two games following his match-winning hat-trick against Blackburn last Saturday.
Wolves could have drawn level immediately, but again Krul was the difference, this time displaying his speed and agility.
Diving to his left to another Doyle strike, Krul was forced to use his outstretched right foot to make the all-important save with the effort deflecting off Steven Taylor.
From the rebound it was the other Taylor in Newcastle's defence, Ryan, who then bravely threw himself in the way of Matt Jarvis' follow up.
Again it proved crucial because after Hennessey denied Cheik Tiote from 25 yards and Gutierrez scuffed a Danny Simpson cross at the near post when it appeared easier to score, the Argentine at least made amends soon after.
With Wolves struggling to escape their own half, Gutierrez picked up a stray pass from Karl Henry, who was later ironically cheered by the home fans when he was substituted on the hour due to his recent poor performances.
Gutierrez first evaded three tackles before cutting inside skipper Roger Johnson, prior to applying a cool incisive finish with a left-foot shot beyond Hennessey from 12 yards.
Wolves then went into the dressing room at the break knowing it was not going to be their day when referee Mark Halsey turned away two penalty appeals in a matter of minutes.
The first was obvious as Steven Taylor's challenge on O'Hara was inside the area, only for Halsey to award a free-kick outside, to the frustration of all within the Wolves' camp.
A neat free-kick between Jarvis and O'Hara resulted in a looping shot from the latter that forced Krul into an uncomfortable, but necessary tip over.
The boos at the half-time whistle from the home faithful signalled the dejection at their side's continuing slide following a positive start to the campaign when they began with two victories.
After the break Wolves were the better side, more aggressive and purposeful, although they should have been 3-0 down in the 65th minute, only for Ba to curl inches wide a low shot.
With Wolves in desperate need of a lifeline, they then found Krul at his best in pulling off a double save in a matter of seconds to thwart Fletcher and 58th-minute substitute Adam Hammill.
It was not until three minutes from time Krul was finally beaten, with Fletcher making it eight goals in his last 12 league games with a diving header onto a Hammill cross.
Then in the first of five minutes added time, Wolves thought they had grabbed a dramatic equaliser.
However, Doyle's close-range effort was ruled out as the cross in the build up was adjudged to have gone over the dead-ball line.
NEXT NEWCASTLE UTD MATCH:
TOON v TOTTENHAM HOT.
Sunday October 16th KO 4pm
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NEWCASTLE UNITED 20011/12
PREMIER LEAGUE
WOLVES 1 NEWCASTLE 2 (Ba, Gutierrez)
Krul, Simpson, Steven Taylor, Coloccini, Ryan Taylor, Obertan (Marveaux 90), Cabaye (Guthrie 89), Tiote, Gutierrez, Best, Ba (Lovenkrands 71).
Subs Not Used: Elliot, Santon, Ben Arfa, Sammy Ameobi.
NEWCASTLE 3 BLACKBURN 1 (Ba 3)
Krul, Simpson, Steven Taylor, Coloccini, Ryan Taylor, Obertan, Cabaye, Tiote, Gutierrez (Marveaux 84), Ba (Ben Arfa 74), Best.
Subs Not Used: Harper, Guthrie, Lovenkrands, Perch, Sammy Ameobi.
ASTON VILLA 1 NEWCASTLE 1 (Best)
Krul, Simpson, Steven Taylor, Coloccini, Ryan Taylor, Obertan, Cabaye, Tiote, Gutierrez (Sammy Ameobi 85), Best (Shola Ameobi 69), Ba (Marveaux 80).
Subs Not Used: Elliot, Guthrie, Lovenkrands, Perch.
QPR 0 NEWCASTLE 0
Krul, Simpson, Steven Taylor, Coloccini, Ryan Taylor, Obertan (Sammy Ameobi 88), Cabaye, Tiote, Gutierrez, Best (Marveaux 82), Shola Ameobi (Ba 64).
Subs Not Used: Elliot, Santon, Guthrie, Lovenkrands.
NEWCASTLE 2 FULHAM 1 (Best 2)
Krul, Simpson, Steven Taylor, Coloccini, Ryan Taylor, Lovenkrands (Ba 62), Cabaye, Tiote, Gutierrez, Obertan, Best (Vuckic 78), Vuckic (Smith 85).
Subs Not Used: Soderberg, Marveaux, Sammy Ameobi, Ferguson.
SUNDERLAND 0 NEWCASTLE UTD 1 (R Taylor)
Krul, Simpson, Steven Taylor, Coloccini, Ryan Taylor, Tiote, Cabaye (Williamson 85), Barton, Obertan (Gosling 85), Gutierrez, Shola Ameobi.
Subs Not Used: Harper, Lovenkrands, Ba, Best, Marveaux.
NEWCASTLE 0 ARSENAL 0
Krul, Coloccini, Steven Taylor, Ryan Taylor, Simpson, Barton, Cabaye (Lovenkrands 81), Tiote, Gutierrez, Shola Ameobi (Best 73), Ba (Obertan 46).
Subs Not Used: Forster, Williamson, Gosling, Sammy Ameobi.
CARLING CUP
NOTTINGHAM FOR. 3 NEWCASTLE 4 (AET) Lovenkrands 2, Simpson, Coloccini
Elliot, Simpson, Coloccini, Perch, Ferguson, Abeid, Guthrie, Gosling (Shola Ameobi 70), Marveaux, Ben Arfa (Sammy Ameobi 70), Lovenkrands (Obertan 80).
Subs Not Used: Krul, Best, Dummett, Henderson.
SCUNTHORPE 1 NEWCASTLE 2 AET (R Taylor, Sammy Ameobi)
Krul, Simpson, Coloccini, Williamson (Steven Taylor 45), Ryan Taylor, Marveaux, Gosling (Vuckic 70), Cabaye, Lovenkrands, Best, Ba (Sammy Ameobi 65).
Subs Not Used: Soderberg, Abeid, Smith, Ferguson.
PRE-SEASON FIXTURES
NEWCASTLE 0 FIORENTINA 0
(Ab 63 mins)
Krul (Forster 46), Simpson, S Taylor, Coloccini, Enrique, Gosling (Ba 46), Cabaye, Vuckic, Jonas (Marveaux 46) Lovenkrands (R Taylor 61), Best (Shola Ameobi 46).Subs: Sammy Ameobi, Ranger, Tavernier, Williamson.
LEEDS UTD 3 NEWCASTLE 2 (S.Taylor, Vuckic)
Forster, Cabaye, Williamson, Barton, Simpson, Gosling, Gutierrez, Ba, Shola Ameobi, Taylor, Tavernier. Subs: Krul, Taylor, Best, Vuckic, Sammy Ameobi, Dummett.
COLUMBUS CREW 0 NEWCASTLE 3 (Ameobi, Coloccini, Vuckic)
Harper; Tavernier, S Taylor, Coloccini (Dummett, 54), Enrique; Gutierrez (Abeid, 85), Tiote (Smith, 62), Gosling, Marveaux (Vuckic, 76); Ameobi (Best, 75), Ba. Subs not used: Forster, Krul.
ORLANDO CITY 1 NEWCASTLE 0
Forster; R Taylor (Enrique, 26), S Taylor, Coloccini, Tavernier; Gosling (Vuckic, 71), Smith (Abeid, 74), Tiote, Gutierrez; Best (Ba, 74), Lovenkrands (Ameobi, 74). Subs not used: Krul, Harper.
SPORTING KANSAS 0 NEWCASTLE 0
Krul, Gosling, Coloccini, S Taylor, R Taylor, Marveaux (Tavernier 46), Tiote (Abeid 46), Ben Arfa, Gutierrez, Ba (Best 72), Lovenkrands (Smith 46).
DARLINGTON 0 NEWCASTLE 2 (Barton, Sammy Ameobi)
Forster; Simpson (Dummett), S Taylor (Tavernier), Williamson (Henderson), Ferguson (R Taylor); Barton (Abeid), Guthrie (Cabaye, Donaldson), Smith (Gosling), Vuckic (Sammy Ameobi); Ben Arfa (Richardson), Best (Ranger). Subs not used: Soderberg, Newton.