The Board has decided to confer on Tata the honorary title of Chairman Emeritus, Tata Sons said in a statement.
"The Board of Directors of Tata Sons today announced the appointment of Cyrus P Mistry as the Chairman of the Board after Ratan N Tata retires on December 28, 2012," it added.
Mistry, 44, was chosen as Tata's successor in November last year and was appointed Deputy Chairman of Tata Sons, whose board he had entered in 2006.
Mistry belongs to the Shapoorji Pallonji & Co, a leading construction firm. His family is the single largest shareholder in Tata Sons with 18 per cent stake.
Earlier this month, Tata Motors had appointed Mistry as its Chairman with effect from December 28 after retirement of group chief Tata.
Mistry has also been appointed as the Chairman of Tata Steel and Tata Chemicals.
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Last month, Tata had stepped down as Chairman of Tata Global Beverages, making way for successor Mistry, who was also inducted into the board of Indian Hotels Company. Tata Consultancy Services had inducted him as Deputy Chairman.
Tata Sons is the promoter of the major operating Tata companies and holds significant shareholdings in these firms. About 66 percent of the equity capital of Tata Sons is held by philanthropic trusts endowed by members of the Tata family.
It owns the Tata name and several Tata trademarks, which are registered in India and around the world.