McLeod pounced from close range in the 22nd minute to seal the rock-bottom Dons' first win in 11 league games in front of 7,670 fans.
Dons boss Danny Wilson made four changes to the team that lost 2-0 at Barnsley a week-and-a-half ago, with Ben Harding handed his first start of the season in midfield at the expense of Nicky Rizzo.
Craig Morgan replaced Mark Ricketts at centre-half, while Matt Baker wasn't even in the squad after losing his place in goal to 19-year-old Fulham loanee Ricardo Batista.
Ben Chorley and Wade Small missed out with bans, while McLeod came back from suspension up front and Trent McClenahan returned at right-back in a 4-3-3 formation.
Forest started brightly and Grant Holt wasted a good chance in the 10th minute when he raced onto Sam Clingan's flick but dragged his angled drive badly across the face of goal.
But the Dons got to grips with their new formation and Harding lashed Scott Taylor's cut-back just over the bar from the edge of the box in the 16th minute, before McLeod put them ahead in the 22nd minute.
Harding delivered a delightful curling cross from the corner of the box and McLeod stole in to head his 13th goal of the season past Forest goalkeeper Paul Gerrard from five yards.
Dons keeper Batista comfortably saved Holt's far post header from Ross Gardner's cross in the 39th minute as Gary Megson's men tried to respond before the break, but the hosts defended resolutely to hold out until half-time.
Milton Keynes came out fired up for the second half and Morgan fired just wide from Dean Lewington's corner in the 50th minute, before Forest had a strong penalty appeal waved away at the other end in the 61st minute.
Jack Lester latched on to a loose ball in the box and as he pulled the trigger he was scythed down by Dons defender McClenahan, but Forest's strong protests were ignored.
Chelsea loanee Filipe Morais came on for his Dons debut half an hour from the end and after running the ball the full length of the pitch from a Forest corner, the skilful winger sliced just wide from the edge of the box in the 75th minute.
Forest substitute Eugen Bopp had a rasping 30-yard free-kick well saved by Dons keeper Batista eight minutes from the end as the visitors pressed for an equaliser, but they created little else in the closing stages as the visiting fans called for Megson's head.