Goals from Nick Barmby, Caleb Folan, Richard Garcia and Nathan Doyle have helped Hull reach Wembley for the first time in the club's 104-year history and set up a Coca-Cola Championship play-off final clash against Bristol City on May 24.
Barmby cancelled out Darius Henderson's opener as Watford briefly threatened a stirring comeback in the semi-final second leg at a packed KC Stadium before succumbing to a convincing aggregate defeat.
Substitute Folan climbed off the bench to add his side's second after former England international Barmby had notched his second goal against Adrian Boothroyd's side in the space of four days.
Garcia and Doyle then grabbed a goal apiece late on as Hull romped to victory to spark a pitch invasion at the full-time whistle.
Tigers boss Phil Brown will take the majority of the plaudits after guiding a club seemingly in freefall when he took charge in December 2006 to safety last season and now to within one game of securing promotion to the Barclays Premier League.
Perhaps even more poignant is the fact it was two Hull-born players, Barmby and Dean Windass, who scored the goals over the two legs that in the end sent their hometown club to Wembley.
As for Watford and boss Boothroyd, they are left to reflect on a run of one win from 16 games which scuppered any hopes of an immediate top-flight return.
Despite starting the evening with the comfort of a two-goal cushion following a convincing 2-0 win in the first leg on Sunday, Hull was poor early on and fell behind 1-0 on the night.
However, when Garcia looped a goalward header over the advancing keeper and the outstretched Barmby bundled the ball over the line from right underneath the crossbar, the home side's nerves heading into the interval were eased.
Barmby's equaliser galvanised Brown's men and they looked more comfortable in possession after the restart.
The Tigers finished with a flourish as Garcia scampered through the Watford defence and slotted home from 14 yards after 88 minutes, before substitute Doyle's deflected effort from 12 yards completed the scoring barely a minute later.