The Boro skipper made it eight from eight from the spot a minute before half-time at Griffin Park on Saturday to fire Aitor Karanka’s in-form side back to within a point of leaders Bournemouth.
They also completed the double over the Bees this term, but were made to work far harder for the three points than they had when dishing out a 4-0 thrashing on Teesside in September.
For although Middlesbrough arrived in west London fresh from their shock FA Cup win at Premier League champions Manchester City last weekend, they found last season’s League One runners-up a far trickier proposition in the opening stages.
Brentford’s top scorer Andre Gray should have put them ahead after 10 minutes but planted his header wide six yards out from Alex Pritchard’s cross.
Moments later, a short free-kick from Pritchard found Spanish midfielder Jota 15 yards out and his powerful shot was tipped over the crossbar by Dimi Konstantopoulos.
And from the resulting corner, defender James Tarkowski’s goalbound header was blocked on the line by Leadbitter.
Stuart Dallas was next to try his luck, once again set up by Pritchard, only to see his low, curling drive beaten away by the diving Konstantopoulos.
But Brentford were left counting the cost of their missed chances when Ben Gibson launched the ball forward shortly before half-time.
Bees defender Harlee Dean let the ball sail over him, blissfully unaware that Patrick Bamford had run in behind and David Button charged out of his goal to bring down the on-loan Chelsea midfielder.
Button escaped with a booking but spot-kick expert Leadbitter punished the home keeper further by sending him the wrong way for his 12th goal of the season.
After the break, Boro’s Jelle Vossen twice went close with headers and then produced a superb through-ball for Albert Adomah, only for the Ghanaian to blaze his shot over.
At the other end, Dallas crashed a volley narrowly the top and drove inches wide from long range, while Gray wriggled clear of Kenneth Omeruo only to shoot straight at Konstantopoulos.
In stoppage time, another Dallas volley was deflected over and Konstantopoulos denied Jonathan Douglas from point-blank range as miserly Boro held out for a seventh clean sheet in their last eight games and took another big step towards the Premier League.