The Redeyes survived an extra time thriller to defeat Rennie by nine points at Deniliquin's Memorial Park on Sunday.
After holding a three goal lead during the final term Blighty came under attack, with the Hoppers bringing the margin back.
When Rennie kicked a goal late in the quarter, the scoreboard read that scores were level.
In a final foray forward the Redeyes were desperate to score, with Beau Close booting what was thought to be a match-winning behind as the final siren sounded.
While Blighty celebrated it was confirmed by the goal umpires that the scoreboard read the wrong score and that scores were level at the end of the game, meaning the sides would have to do battle in overtime.
The Redeyes regained their composure, having most of the play in extra time, but couldn't put the Hoppers away with two missed shots on goal.
Blighty's Tristan Wilson finally broke through for the Redeyes, with a dribble kick rolling through for a major during the first half of extra time.
The second half of extra time saw the ball in between the two 50m arcs with Blighty holding on to book their spot in the decider.
Aaron Litchfield was arguably Blighty's best, playing an impressive game at full back.
Tyler Amor-Beale was solid with two majors running from half back, while onballers Josh Peers, Brent Mitchell and Wilson, along with wingman Luke Charlton also among the best.
Final score, Blighty 9.11 (65) to Rennie 9.2 (56).
Blighty coach Kyel Bain said he was extremely proud of his side's efforts after the game.
"It was an absolutely outstanding effort by the boys," he said.
"The way we just kept going again and running and carrying was great.
"It's not just about the team now, it's more about the community with the drought... it gets the community up and about.
"It's been about 19 years (since our last grand final at senior level) so it's exciting.
"I've never played in or been involved in a grand final. I would've only been about 12 years-old when we last played in one."
Sunday's result was a true testament to Blighty's resolve, having to overcome the mental hurdle of playing extra time after thinking they had won.
Despite Rennie having more of the play in the latter stages of the fourth quarter, Bain said he was confident his side could grind out the win.
"I said to them before we went into extra time that it was in our hands as to where we wanted to go," he said.
"I knew they would find another gear, as they have all year.
"Aaron Litchfield was solid at full back and Tristan Wilson was outstanding.
"I thought he (Wilson) broke his neck at one stage, but he got up and he ended up kicking the winning goal.
"Brent Mitchell was a workhorse, and noone could catch Luke Charlton out on the wing.
"Just have to get the twos train to keep rolling and hopefully we can get the old fellas to reach the ultimate goal."
The Redeyes will face-off against Waaia in the grand final at Berrigan on Saturday.