The 27-year-old from the Isle of Man privately expressed a desire to move on in July at the Tour de France, before going public in September, believing Team Sky's stated ambitions and his own no longer matched.
Earlier this week Cavendish was preparing for a second season with Team Sky after protracted talks over an early termination broke down.
Press Association Sport understands Team Sky relented and waived a release fee, allowing the Manxman to move on and sign a three-year deal with the Belgian team.
Cavendish said: "After a year of being part of the successes at Team Sky I've decided to leave to join Omega Pharma-QuickStep Cycling Team to pursue different goals.
"It's been an incredibly fun year riding with friends I've grown up with but I'm super excited about riding with old friends and team-mates in one of the most successful and established teams in cycling.
"I believe in the team's project and I'm thrilled to be a part of it."
The Manxman, who won the points classification green jersey at the 2011 Tour, claimed the world title in September 2011 and joined Team Sky a few weeks later.
He was part of the team which helped Bradley Wiggins become the first British winner of the Tour and won the final stage for a fourth successive occasion in Paris. It was his 23rd Tour stage win, taking him to fourth in the all-time list and within reach of Eddy Merckx's record haul of 34.
Cavendish was already determined to leave, believing a Team Sky bid for the yellow jersey and the green jersey in the same year was no longer on the agenda.
Having joined a British team, with many of his friends and colleagues from British Cycling, Cavendish discovered overall victories were the priority.
He suffered disappointment in the Olympic Games road race, his major objective for the season, and spoke publicly of his wish to leave Team Sky on the eve of the Tour of Britain last month, comparing the situation to a long-distance relationship.
He won the final stage of the Tour of Britain to Guildford for his 15th success of the season in his last race in a Team Sky jersey.
Team Sky principal Dave Brailsford paid tribute to Cavendish.
"Mark has been a true champion for Team Sky this year," Brailsford said. "It's been an honour having the rainbow jersey in this team and great to work so closely with a rider I've known since he was a junior.
"He has been a real team player, making history in a Tour de France winning team.
"Cav won 15 races with us, including his first stage race, three Tour stages, and the fourth win in his unbeaten run on the Champs Elysees.
"The sight of him winning in Paris, with the yellow jersey leading out the world champion - both in Team Sky kit - is something you'll never forget.
"We all wish Mark the very best with his future ambitions in a new team and as British rider."
Wiggins added his tribute, with reference to July 22 in Paris when his Tour triumph was confirmed and Cavendish won the stage.
Wiggins wrote on Twitter: "Sad to see my mate Mr Mark Cavendish leaving Sky, it's been a pleasure this year and the highlight leading out the man on the Champs (Elysees)."
Omega Pharma-QuickStep have long been favourites for Cavendish's signature and a place was made vacant on their roster when Levi Leipheimer was sacked for his role in the Lance Armstrong doping scandal.
The Belgian squad have the desire and capability to make the Briton their Grand Tour leader and prioritise stage successes.
Omega Pharma-QuickStep have a number of riders and staff Cavendish has worked with previously, and successfully.
The Manxman won 20 Tour stages and the fabled Milan-San Remo Classic in 2009 while at HTC-Highroad, where he worked with sporting director Brian Holm, who is now at the Belgian team.
Tony Martin, the world time-trial champion, was also a team-mate at HTC-Highroad.
Cavendish knows Irishman Matt Brammeier well from his youth and Andy Fenn is a product of the British system, while he has in the past had a keen rivalry with Tom Boonen.
Cavendish is likely to share leadership responsibilities with Martin and Boonen.