The voting panel of Queensland legends Mal Meninga and Darren Lockyer, and Blues great Laurie Daley adjudged the Queensland prop the most influential player in a Maroons-dominated series after NSW won game three on Wednesday night.
Cotter had earned man-of-the-match honours after the first game, in which he played big minutes following an injury to Tom Gilbert midway through the first half.
Cotter's versatility came to the fore in his first full series for the Maroons - he started in the front and second row across the series and was one of the side's most consistent performers.
"He's an incredible player," Maroons coach Billy Slater said.
"If every team had a Reuben Cotter they'd be in a much better position."
The recognition came after Cotter excelled on debut in Origin I last year, only to be cut down by injury and miss the remainder of the series.
"It's been a great series," Cotter said on Wednesday of his follow-up Origin campaign.
"I just want to say thanks to all the Queensland supporters for coming out tonight, and to the five million back home watching - thanks for supporting us all the way through."
It marks the second successive year a Queensland forward has won the medal, after Patrick Carrigan took it home in his debut series in 2022.
Cotter's teammate in the middle of the park Lindsay Collins was man-of-the-match in the second game in a big win for Queensland at Suncorp Stadium that secured the series.
NSW five-eighth Cody Walker earned the nod as the Blues won 24-10 in Origin III.
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