Mittal's son-in-law Amit Bhatia was brought into the club by Briatore and Ecclestone in December 2007, buying a 20% stake and joining the board of directors.
Current managing director Ishan Saksena replaces the 61-year-old Italian, and Gianni Paladini will resume his role as chairman of the club.
Briatore and Ecclestone will retain their shareholding in the Loftus Road outfit.
"My three years as chairman of QPR have been an exciting and incredible experience. I'm proud to have helped save this historical club and to have contributed in paving the way to its future success," said Briatore.
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