Kildare failed to score from the 42nd minute onwards against Longford but did enough to claim their first Cadbury Leinster Under-21 Football title since 2008, while Cavan and Donegal advanced to an Ulster final meeting on April 17.
A 31st minute penalty goal from Paddy Brophy proved to be the difference as Kildare claimed a 1-12 to 0-12 final victory over first-time title seekers Longford tonight.
Sean Hurley, Fionn Dowling, Paul Cribbin, Brophy and Niall Kelly were in superb form as Kildare led by 0-9 to 0-5 at the break, with Mark Hughes and Robbie Smyth keeping Longford in touch.
Kildare moved eight points clear within two minutes of the restart thanks to Brophy's penalty goal and a Padraig Fogarty point, but Longford failed to give up.
Goalkeeper Paddy Collum was solid in the opening half, pulling off a 12th minute save from a Fogarty goal shot and he continued to prove strong on the restart.
Longford knuckled down and outscored Kildare by three points to one between the 34th and 39th minutes, with Hughes, Darren Gallagher and Smyth on target.
A 42nd minute Thomas Moolick point gave Kildare a 1-12 to 0-8 lead, but Kieran McGeeney's side suddenly became wasteful in front of the posts.
Longford upped their game with Barry McKeon, Gallagher, Darragh Bennett and Daniel Mimnagh working hard.
A trio of points cut the gap to four by the 54th minute, but Longford were unlucky not to reduce the gap even further at this stage - Hughes failed to put the ball in the net despite an open goal being at his mercy in the 52nd minute.
An injury to Robbie Smyth, which forced the exit of the Abbeylara clubman in the 56th minute, was another setback for Longford.
Five minutes of injury-time followed during which Longford cutting the gap to a goal, but Eoghan McCormack's side could not find further scores as Kildare held out for their 10th provincial crown at this age-grade.
After the game Kildare captain Tommy Moolick received the cup from Leinster GAA Chairman Martin Skelly, while fellow midfielder Seán Hurley picked up the man-of-the-match award.
Meanwhile, Cavan and Donegal overcame Down and Derry respectively at the semi-final stage of the Cadbury Ulster Under-21 Football Championship tonight.
Cavan booked their place in their fourth provincial decider in-a-row, following a comfortable 1-12 to 0-6 victory over Down at Armagh's Athletic Grounds.
The reigning champions were always in control and led by 0-9 to 0-2 at the interval.
Cavan moved 10 points clear within a minute of the restart thanks to a Paul O'Connor goal and never looked troubled, despite Down outscoring them by four points to three in a low-scoring second half.
A repeat of the 2010 Ulster U-21 final will take place later this month after Donegal overcame a determined Derry side to secure a 2-11 to 0-15 semi-final win over the Oak Leafers.
The sides were tied at 1-5 to 0-8 at half-time, with Odhran MacNiallias fisting home an early goal after a high ball into the square by Paddy McBrearty.
Derry fought back with Ballinderry clubmen Aaron Devlin and Ryan Bell putting in excellent work to help tie the game at the break, although Derry kicked six first half wides.
McBrearty was again involved in Donegal's second goal, which arrived early in the second period after he played in Caolan Ward who finished to the net.
Donegal moved 2-7 to 0-8 ahead five minutes into the half, but Ciaran Conway, Conor Kearns and Ryan Bell helping to reduce the gap for Derry to four points with eight minutes remaining.
Bell continued to eat into Donegal's tally late on, but the Tir Chonaill youngsters held out for a two-point success which gives them a shot at repeating the county's 2-8 to 0-7 final victory over Cavan from 2010.