McNish, who won the prestigious race this year to add to victories in 1998 and 2008, achieved 66 podium finishes including 29 outright wins after joining the Audi team in 2000, will stay on in a technical capacity with the team.
The Dumfries-born 33-year-old started his career in karting, winning three British titles and third place in the 1985 World Championship, and went on to Formula One, where he drove a full race season for Toyota in 2002.
McNish told his official website: "I've had a fantastically successful time with Audi and feel it's the right time to step back from Le Mans sports-prototype racing and to look at other opportunities.
"As a racing driver it's important to stop at the right time when I'm still fast and capable of doing the job and the timing feels right after winning Le Mans for a third time this year and claiming the world title.
"I've won the championships and race I wanted to win and frankly there's no better way to end my Audi sportscar race career than going out as a world champion.
"We've ticked all the boxes and I ticked my personal ones too but now the time is right to hand over to the young guys.
"There are some great new drivers coming through and they need an opportunity just like I did. I'm looking forward to being part of Audi Sport in the future to ensure that these young drivers have the same level of fun and success that I have enjoyed over the years.
"I celebrate my 44th birthday later this month and I've only ever been involved in racing to win. Winning is the sole reason I went racing and the investment of time, energy, mental and physical attention plus the sacrifices for my family can now be adjusted."