The 35-year-old, who also captained England, retired from playing in May after racking up more than 500 games for Leeds across an 18-year spell between 1997 and 2015.
Sinfield, who spent last year with rugby union club Yorkshire Carnegie, will help players find new careers after retirement, as well as work on a four-year plan for the England team ahead of the 2021 World Cup.
"I'm delighted to be joining the RFL," said Sinfield. "I am very grateful for the opportunity and really excited about working with some talented people. I'm aiming to help our sport achieve great things in the coming years both domestically and internationally.
"I believe it's important for our sport to have a strong international setup. With the World Cup next year in Australia and then potentially on home soil again in 2021 the coming years could be really positive for Rugby League.
"There are some incredible personalities in Rugby League who have a great mix of experience and knowledge. Hopefully by taking on this role it will encourage other players, both former and current, who have aspirations of furthering their careers to come and pursue a new pathway at The RFL."
RFL chief executive Nigel Wood added: "I'm pleased that we have been able to attract someone with the experience and calibre of Kevin Sinfield to join the RFL.
"The 20 years Kevin has spent as a player at the very highest level of the game will provide us with incredible insight and having spoken to him at length about the opportunity to work with us, I know that he is determined to make as much of a difference off the pitch to the sport of Rugby League as he did on it.
"This appointment is one of a number of significant executive announcements that we will be making in the coming months."
Sinfield won seven Super League titles and came second in the BBC's Sports Personality of the Year vote in 2015.