The 32-year-old beat off competition from Wigan full-back Sam Tomkins, the 2012 Man of Steel, and Australians Cameron Smith, Ben Barba, Cooper Cronk and Nate Myles to lift the prize, awarded annually to the game's greatest player by Rugby League World magazine.
Sinfield skippered the Rhinos to a sixth Super League title in nine years, famously overcoming a sickening head knock to be named man of the match in his side's win over Warrington, and celebrated his appointment as national captain by leading England to victory in the 2012 autumn international series.
He also led Leeds to World Club Challenge success over Manly Sea Eagles and to a third consecutive Challenge Cup final appearance at Wembley in 2012.
Sinfield, who is expected to lead England in the 2013 World Cup, is the first Englishman to win the Golden Boot since former Wigan and Great Britain skipper Andy Farrell triumphed in 2004.
Ellery Hanley (1988) and Garry Schofield (1990) are the only others to win the award since it was introduced in 1984.
Rugby League World editor John Drake said: "The British game can and does still produce individuals of world-class ability. Kevin Sinfield is one such player and it is right that his towering achievements in 2012 should be recognised with the Golden Boot."
Martyn Sadler, chairman of League Publications Ltd, said: "In the Grand Final Sinfield kicked five out of five, from all over the pitch, and that after he had been knocked out earlier by a challenge to the head.
"What he did in that game goes beyond what could reasonably be expected, even of a Golden Boot winner. Twice injured with brutal clashes that epitomise the sport, he simply shrugged off those knocks, got up and got on with his own game, setting an example for his colleagues to follow.
"After the game he denied that the head clash had marred the game for him. That demonstrates another quality that marks out great players, almost unbelievable courage and toughness."
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