Donegal hit three points in injury-time to edge out Mayo 0-13 to 0-10 in a tense Allianz NFL Division 1 final.
Colm McFadden (left) tries to hold off Mayo's Liam O'Malley
Brian McIver's side hit the opening four points at Croke Park and they held a 0-7 to 0-5 advantage at the break.
However, Mayo dominated after half-time and Andy Moran wasted a glorious goal chance which would have put them ahead.
But Donegal regrouped during the eight minutes of added time with subs Eamon McGee, Rory Kavanagh and Adrian Sweeney swinging over glorious points.
Donegal made late changes to the team announced on Friday with Brendan Devenney and Paddy McConigley replacing Kevin McMenamin and Thomas Donoghue.
The north west county started in brisk fashion and Colm McFadden had an immediate goal chance after a superb pass from Devenney but the effort was diverted out for a 45.
However, Donegal continued to put the Mayo defence under pressure and Brian Roper struck over two superb points as they made their early dominance count.
McFadden slotted another score after his delightful dummy and Donegal were four ahead when Kevin Cassidy pointed after good work by Devenney.
However, Mayo hit four of the next five scores with Conor Mortimer pointing two frees and the impressive duo of Alan Dillon and Pat Harte also getting on target.
Roper's third score of the first half edged Donegal two ahead and the margin was the same at the break as Brian McIver's side led 0-7 to 0-5.
Brian Roper (right) beats Peadar Gardiner to win possession
By that stage, Devenney's injury problems had forced his departure with McMenamin coming on.
McFadden's free was the first score of the second half but Mayo began to get a grip on proceedings in the middle third of the field and two Neil McGee fouls gifted points to free-taker Mortimer.
Ciaran Bonner's score from play re-established a two-point lead for Donegal but by now, Mayo were firmly in the ascendancy and two more Mortimer frees brought the sides level by the 54th minute.
A rare Donegal attack saw McMenamin restoring Donegal's lead but they came the crucial moment of the match when Andy Moran was presented with a glorious goal chance for Mayo.
The ball came to him quickly but he should have hit the in the net instead of blazing over the bar to level the contest.
Play was then held up for several minutes after Donegal's Ciaran Bonner had been the victim of a crunching but totally legitimate challenge from David Heaney.
The halting of the action probably boosted Donegal as they somehow resolved to summon up a huge effort during the protracted injury-time.
Kavanagh struck Donegal ahead in the second minute of injury-time and Eamon McGee charged up the field moments later to loop over a sensational score from 45 metres.
With Donegal tails up, veteran sub Sweeney then got in on the act to swing over another marvellous score and Mayo knew that it wasn't going to be their day.
The win was Donegal's first National League title while Mayo were left to rue another Croke Park disappointment.
Donegal: P Durcan, N McGee, P Campbell, K Lacey, P McConigley, B Monaghan, B Dunnion, N Gallagher, K Cassidy, C Bonner, B Roper, C Toye, B Devenney, C McFadden, M Hegarty.
Mayo: D Clarke, L O'Malley, J Kilcullen, K Higgins, E Devenney, BJ Padden, P Gardiner, P Harte, D Heaney, G Brady, K O'Neill, A Moran, M Conroy, A Dillon, C Mortimer.