While no financial details have been announced, media reports have said the new deal would be worth around $30 million a year, compared with the $10 million a year agreement Federer had with Nike.
The 37-year-old, who has won 20 Grand Slam singles titles -- a men's record -- signalled the end of his association with Nike in July when he walked out onto Wimbledon’s Centre Court dressed in Uniqlo apparel.
Federer said the belief shown in him by Uniqlo's CEO Tadashi Yanai and Executive Creative Director John Jay had been key.
"John Jay in New York, where I had an event there, said it very nicely: 'One day I will retire from tennis but I will not retire from life,'" said Federer, who was presented as Uniqlo's new global brand ambassador.
"Life will go on and Uniqlo and Mr. Yanai believed in me very strongly as being very important to their brand, even though maybe my playing days are going to come to an end at some point."
By incorporating Federer in their LifeWear range, Uniqlo appear to see the Swiss as a brand off court as much as on it.
One of Federer's goals after he retires is to develop the charity work started through his foundation, which aims to empower children in poverty through education, and he said Uniqlo shared that vision.
“Some people cannot go to school, even though they want to, some people do go to school but do not get a quality education and so this is where the Roger Federer Foundation has tried to make a difference in the region of Southern Africa,” he said.
Federer's switch to Uniqlo comes at a boom time for Japanese tennis after Naomi Osaka claimed the country’s first Grand Slam singles title at the U.S. Open last month.
Federer, a five-time winner at Flushing Meadows, praised the mental strength of the 20-year-old, who has also qualified for the season-ending WTA Finals.
"I think winning Indian Wells helped her to believe that she could also win another big title,” said Federer, who is planning an exhibition match in Japan next year.
“I think she is a champion in the sense that she doesn’t shy away from the big stage. Indian Wells is the second biggest tennis court we have in the world and the U.S. Open is the biggest one.
"She succeeded in both of them and that shows a winner's mentality."
(The story has been refiled to clarify in paragraph 3 that Federer's 20 grand slam singles titles is a men's record)
(Editing by Peter Rutherford)
