A drop goal from Danny Brough was all that separated the sides after one of the most gripping Challenge Cup finals in history as Hull lifted the trophy for the first time in 23 years.
Super League champions Leeds suffered cup final heartbreak for the second time in three years at the Millennium Stadium after conceding a try to Hull's semi-final hero Paul Cooke three minutes from the end of a thrill-a-minute clash in Cardiff.
In the last of a series of twists and turns that will make rugby league's first mid-summer final one of the most memorable, Brough kicked his fourth conversion to secure only a third triumph in Hull's 109-year history and their first since an Elland Road replay in 1982.
For a long time, another replay was a distinct possibility as the sides fought tooth and nail for supremacy but Brough, who was combining rugby league with a plumbing trade two years ago, had the foresight to put over an all-important one-pointer on the hour.
The outcome was another landmark in the fairytale coaching career of John Kear, who famously guided even bigger underdogs, Sheffield Eagles, to victory over Wigan in 1998 but it all ended in tears once more for Leeds skipper Kevin Sinfield, who found little consolation from the Lance Todd Trophy as man of the match.
In a quite extraordinary climax to a remarkable match, veteran Papua New Guinea winger Marcus Bai looked to have redeemed himself with the match-winning try as Leeds fought back in style.
The 32-year-old Bai grabbed a try 13 minutes from the end to atone for a calamitous defensive blunder that would otherwise have scarred his Rhinos career forever but, in the end, it counted for nothing as Leeds suffered a third final defeat in six years.
Both sides had to overcome adversity before carving out their place in history. Leeds, who surprisingly dropped veteran prop Barrie McDermott, gambled on the fitness of centre Keith Senior but the Great Britain international struggled with his twisted ankle throughout the first half and it was no surprise when he failed to appear after the break.
Hull went into the game without their former Warrior and full-back Shaun Briscoe, who is recovering from a appendix operation, and they felt his absence on 11 minutes when Leeds scored the game's first try.
Left winger Gareth Raynor compounded a lack of communication with makeshift full-back Nathan Blacklock as they vied for for Sinfield's high kick by tugging at the shirt of Mark Calderwood and video referee Bob Connolly had no option but to award the Rhinos winger his 32nd try of the season.
Hull were unfortunate with a wicked bounce as, not for the first time, the ball played tricks on the unpredictable and, at times treacherous surface.
But Leeds helped their opponents back in the game with a series of handling errors inside their own half and, after Hull stand-off Richard Horne had been held inches short of the line, the scores were levelled on 23 minutes thanks to some superb quick-thinking.
The try was created with a clever flick-on by centre Richard Whiting into the arms of winger Motu Tony, who had the presence of mind to chip over Marcus Bai and claim his fifth try of the season, which was goaled by Danny Brough.
That was just the encouragement Hull needed as they stepped up the pressure and the video referee was twice more called on to rule out possible scores by Kirk Yeaman and Blacklock.
Somehow the Leeds defence managed to hold firm until half-time, when the scores were locked at 6-6, but Hull went in front for the first time five minutes into the second half.
Tony set up the position with a crucial interception and, after Garreth Carvell was held up short by the posts, the ball was flung wide for Blacklock to get Raynor over with a wonderful pass out of the tackle.
A patched-up Sinfield, who was easily the Rhinos' best player, carved out a try for prop Danny Ward on 49 minutes and levelled the scores for a second time with the goal but it was a score against the run of play.
The Black and Whites regained the lead with Richard Whiting's fortuitous score, with Bai foolishly passing behind his own line, and Brough maintained his 100% accuracy with his third conversion before putting his side two scores ahead with a drop goal just short of the hour.
There were signs of nerves, with both sides failing to find touch with penalty kicks, and the drama heightened on 67 minutes when Calderwood took Sinfield's pass from a scrum deep inside his own half and slide between Blacklock and Tony for a glorious second try.
When Bai outjumped Tony to touch down 13 minutes from the end and Sinfield kicked his fourth goal, Leeds looked certain to add the cup to the World Club Challenge and Super League trophy as they led 24-19.
But Cooke had the last say when he dummied his way through a tiring Rhinos defence to send the 20,000 Hull fans into raptures.
Leeds Rhinos must now recover quickly after two defeats in two weeks as they travel to the JJB Stadium next Friday to take on Wigan Warriors.
Tickets are now available for the last two home games of the season against Leeds Rhinos on 2nd September, and against St Helens on 9th September. These are available from the JJB Stadium Ticket Office, Ticket Hotline on 0870 11-22-552, online BY CLICKING HERE and also from the Leeds and St Helens club ticket offices.