Sinfield announced he will retire as a Leeds Rhinos player this autumn to join their rugby union sister club Yorkshire Carnegie.
Sinfield made his Rhinos debut in 1997 and has captained the current Challenge Cup holders to six Super League Grand Final wins, three World Club Challenge titles and victory at Wembley last year.
The 34-year-old, who needs four points to reach a career total of 4,000, described it as the “toughest decision of my career”.
Sinfield added: “I know the time is right for me to finish my time in rugby league and embark on a new challenge with Yorkshire Carnegie.
“My goal now is to do whatever I can to make sure we have further success this year and finish the season - and my Rhinos career - on the best-possible note.”
Rhinos chief executive Gary Hetherington described Sinfield as “an inspirational leader” and admitted the success of the past decade would have been impossible without him.
“We’re pleased he will remain at Headingley Carnegie,” Hetherington said of Sinfield, who was contracted for 2016.
“If any player in the history of the club deserves the right to choose when he moves on to the next stage of his career it is Kevin Sinfield.
“We are happy to agree to his wishes.”
Carnegie executive president Sir Ian McGeechan said Sinfield is “a great addition” to the squad as they aim to return to the Aviva Premiership.