The dark skies saw the match reduced to 18 overs per side but that made no difference as Paul Thwaites' side overtook Chris Larsen's Oakham's 103 with just a matter of balls to spare.
Thwaites was over the moon with his team, which had lost to Ketton in the first round of the tournament, only to reach the semi-finals as the highest scoring losers.
The skipper told the Mercury he hopes the success will lead to more glory for Marko.
He said: "I'm so pleased for everyone involved and it feels fantastic to get back to winning some silverware for Marko.
"I thought we batted and bowled superbly, we showed character and belief and we deserved the victory.
"We have to build on it now. I honestly believe Twenty/20 is the future for the game at this level and it would certainly get my backing, but until the day when that happens we've got to concentrate on the current format.. "
Before the final there had been question marks over whether Tom Flowers, Dilriuk Yathagodawould be allowed to play having failed to make the required number of appearances this season, but with the issue resolved, it was Marko regular Brain Makwana who was the star with an unbeaten 45.
Thwaites said: "Brian played for us in the past and has come back, he is on the committee and he is dedicated to pushing the club upwards.
"His performance was absolutely fantastic and he was delighted."
For Thwaites the success made up for the disappointment of 12 months earlier when Marko were unlucky to lose in the semi-final against Uppingham.
He said: "I felt we deserved a place in the final last year but that's behind us now.
"It's been a really good tournament and we seem to have the players who thrive in this format. Now we can look forward to coming back next year and giving our all to defend this."
As well as the trophy Marko receive £500 of vouchers from Kookaburra to spend on equipment.
Thwaites added: "How it'll be spent I don't know yet, but it'll be used properly.
"We're looking to build on what we have and develop the social side as well because it's a lovely place to play your cricket, but we need to have a set-up like they have at Oakham if we are to go on."
Oakham skipper Chris Larsen was disappointed with the turnout and with his side's performance.
He said: "I think we had about 80 here which is less than last year but the weather was nothing like predicted, which is a shame, but it was a good final.
"All credit to Market Overton because they did a great job but we didn't do ourselves justice with the bat or in the field.
"It's been a good tournament, it's very good for Rutland cricket and now we'll just have to aim to come back and win it next year."
l See page 109 for more photos and a full match report.