Loeb will contest a selected programme of rallies next season, but the ninth successive WRC title he celebrated this year will be his last.
There were emotional scenes at the team as the end of an era arrived with Loeb's 76th career win on the Salou-based WRC finale.
Loeb said: "I have to say a big thank you to everybody in the team, I'm pleased to finish the season and - more or less - my career with a win.
"For sure, the situation is a bit strange to know that I won nine titles in a row and now decided to retire."
The Frenchman admitted to mixed emotions at the end, having driven for the Citroen team for the last 11 years, but he pointed out that the coming World Touring Car Championship entry would keep him busy.
"It's strange," he said, "but on the other side I know I still have some rallies next year and some more plans with Citroen in some other discipline.
"Thank you for everything we have achieved together.
"This marks the close of one chapter, but we have another ahead of us that is about to begin."
In other news, Ford team principal Malcolm Wilson paid tribute to the Blue Oval's commitment to WRC after its last rally in Spain.
Ford announced last month that it would quit the series as title sponsor of the M-Sport run team, ending a 16-year association with the Cumbrian firm.
Jari-Matti Latvala, second on the Spanish event and third in the drivers' championship, also leaves to join Volkswagen for next year.
"16 unbroken years is pretty incredible," said Wilson. "And I have to say a very big thank you to them.
"Of course it's an emotional time, not just because of Ford's decision, but also because Jari-Matti [Latvala] is moving on.
"But nothing stands still. M-Sport has an exciting future ahead and we have to focus on that right now."
Ford's Gerard Quinn added: "We will continue to support M-Sport technically, of course, and drivers of Ford rally cars around the world.
"And who's to say that, in the future, Ford won't step back into the World Rally Championship again.
"It's been a very emotional weekend and I, personally, take a whole load of memories away with me."
Ford won two world titles - in 2006 and 2007 - with M-Sport.