Muller, a three-time WTCC champion, has signed a two-year deal with the French marque.
The 43-year-old has previously competed for SEAT and Chevrolet's works teams, racking up an unparalleled 36 wins, 89 podiums and 19 poles during his eight years in the series.
He has also run away with this year's championship, and with eight races to go has a massive 132-point lead at the head of the standings.
"I am really honoured to represent the colours of Citroen," Muller said.
"It's fantastic that a brand that has won so much in motor sport has decided to join a category where it needs to learn everything.
"And this is a great motivation for me, as I can bring my experience and give my contribution to build a successful programme."
Muller has already tested Citroen's C-Elysee at Paul Ricard, and was a possible catalyst for Loeb's move into the series after inviting the nine-time World Rally champion to test his Chevrolet Cruze at Rockingham two years ago.
While it has dominated rallying in recent years courtesy of Loeb, the WTCC programme represents Citroen's first foray into track racing.
"Throughout its history, be it in cross-country rallies or WRC, Citroen Racing has always sought to recruit the best drivers," Yves Matton, managing director of Citroen Racing, said.
"We have set ambitious goals for our new challenge in WTCC, and the arrival of a driver as experienced as Yvan will help us to make rapid progress.
"He has shown this season that he is at the peak of his powers and that his thirst for wins has never been greater. He will also be an excellent point of reference for Sebastien Loeb.
"The two men are from the same region and have known each other for a long time. Their mutual respect will create a natural cohesion within the team."
The team is expected to run up to three cars during 2014.
Former Formula 1 driver Robert Kubica, who joined Citroen for this year's WRC 2 campaign, is rumoured to be set for a limited WTCC programme with the team next year.
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