Leadbitter, who also netted a stunning 35-yard free kick in the first half, kept his nerve after Adam Reach was fouled in the box by Tommy Smith to score the winner.
It spared Middlesbrough’s blushes after they controlled the second half but seemed set for a draw when Stead equalised with four minutes of normal time remaining.
Top scorer Leadbitter, who has now hit six goals this season, pulled the strings throughout to spoil Chris Powell’s first match as Huddersfield boss.
It was a tasty affair from the off yet, remarkably, nobody was sent off and there were only two bookings for each side.
Jacob Butterfield, who moved to Huddersfield from Boro last month, had already been cautioned for a bad aerial foul on George Friend when Wells acrobatically went close on 11 minutes.
A free kick, given for a foul by Reach on James Vaughan, flicked off Kike and Wells pounced with an over-kick which Dimitrios Konstantopoulos held.
The game nearly boiled over on 17 minutes when Vaughan went in on Konstanopoulos with his foot up after being put in the clear by Wells.
Vaughan’s heavy first touch saw the ball run to the Boro keeper but he kept going and the pair collided heavily.
There was a four-minute stoppage while Konstantopoulos was treated and players from both sides, particularly Lee Peltier and Lee Tomlin, squared up to each other.
Vaughan was lucky to see only yellow but was substituted nine minutes later seemingly due to an injury.
On 25 minutes there were two off the ball incidents in which Friend, who was booked, appeared to elbow Mark Hudson in the face while Kike flattened Conor Coady.
Shortly after Friend was on the receiving end as he was fouled by Wells 35 yards from goal.
From that distance it would take something special to Alex Smithies, but unfortunately for the hosts the ball was at Leadbitter’s feet and he conjured some magic to break the deadlock in style.
Adam Clayton, who left the John Smith’s Stadium to join Boro last month, threatened to make it worse as he jinked into the box past Jack Robinson on 40 minutes, but he fired into the side netting from a tight angle.
The influential Leadbitter and Tomlin combined to put Kike through on 43 minutes and the striker was only denied by a goal-saving parry from Smithies.
Town’s Joel Lynch headed over a Butterfield corner on 29 minutes while the midfielder drew a good save from Konstantopoulos three minutes later after a solo run.
Boro, who had lost their last two games, remained on top in the second half and could have won by more.
Smithies denied Albert Adomah on 57 minutes and then the striker combined with substitute Jelle Vossen on 66 minutes to create a chance for Kike, who fired over.
Huddersfield, without a win at home since the 5-0 rout of Barnsley in March, created little despite the introduction of winger Joe Lolley on 61 minutes.
Belgian Vossen, making his debut on loan from Genk, set up Chelsea loanee Patrick Bamford who drilled wide on 84 minutes.
The late drama then got under way with Stead nodding home the equaliser after good work from Butterfield and Ward.
But just when the Terriers thought they had snatched a draw, Leadbitter stepped up to take full advantage and ensure all three points went back to Teesside.