Shaking with emotion, Thurston was almost lost for words following fulltime. "I'm speechless... I can't believe it," he said. "I love these boys, they've worked so hard, I see it every day. I love the club. Wow, I can't believe it."
After losing the 2005 decider to Wests Tigers and bowing out of the title race in controversial fashion in each of the past three years, the Cowboys would not be denied this time round.
They did it the hard way, falling behind 8-0 after the Broncos claimed an early penalty to Corey Parker and a long-range try to Corey Oates.
The Cowboys hit back with tries to Justin O'Neill and James Tamou but the Broncos edged ahead 14-12 with a Jack Reed try six minutes before halftime.
Jordan Kahu extended their lead with a second-half penalty and the game seemed to have slipped through the Cowboys' grasp before the drama unfolded at the death.
The football action began mid-afternoon as temperatures climbed into the mid-30s, with Penrith beating Manly 34-18 in the Holden Cup decider, before another Queensland side, Ipswich, overcame Newcastle 26-12 in the State Championship.
Earlier, the Nine Network stood down league great Andrew Johns from the grand final broadcast after the former Newcastle captain propositioned a married woman at Toowoomba Airport on Friday.
Johns was not wanted for the match broadcast, after he was forced to apologise to married mother-of-three Helen Wright, who had accused him of being intoxicated and trying to kiss her.
Last night, the main event started at a furious pace, with the Broncos stunning the Cowboys before live-wire hooker Jake Granville sparked their attack to send O'Neill over.
The Broncos were intent on playing at a high tempo but were starved of genuine attacking chances, before losing the lead, when Sam Thaiday slipped off a tackle to allow Tamou to cross.
Brisbane then seized upon a Thurston error, with back-rower Matt Gillett sending Reed in for their second.
The Cowboys threatened to hit back repeatedly through sustained possession but the Broncos were alert to Thurston's favoured left-side options.
Defensive pressure saw Kane Linnett spill the ball with the line beckoning, and Lachlan Coote had a try denied due to a double-movement.
Both sides continued to press for the elusive match-winning score and the Broncos had it in the bag until Feldt's finger-tip effort set up the fairytale finish.
Cowboys 17 (Justin O'Neil, James Tamou, Kyle Feldt tries, Johnathan Thurston 2 cons, field goal)
Broncos 16 (Corey Oates, Jack Reed tries, Corey Parker 1 con, 1 pen; Jordan Kahu 1 con, 1 pen)
