Iconix, the newly formed marketing branch of Saatchi, signed Tendulkar, one of the sport's leading batsmen, after his 10-year contract with the US-based WorldTel expired last year.
"It's great to have a legend like Sachin as the first client of Iconix," said V. Shantakumar, the chief executive officer and managing director of Saatchi's Indian operations.
"Sachin is more than just a cricket player," he said. "He's a role model for young and old India, Shanthakumar said.
"He's still the nation's youth icon and he's still considered by cricket pundits as the world's best batsman. The value he commands comes from the respect and love people feel for him."
Shanthakumar declined to confirm media speculation that the three-year deal was worth 1.8 billion rupees (40 million dollars).
"The amount mentioned is a nice sum, but I am not going to say more," he said.
Tendulkar, who is recovering from a shoulder surgery, and has bees struggling with his form, missed the recent One-day series at home against England and will also sit out of the five One-dayers in the West Indies later this month.
The 33-year-old, whose fitness will be assessed next week, may be available for the four Test matches against the West Indies starting on June 2.
The Mumbai star was delighted to be associated with his new agents.
"I've entrusted Iconix with managing my affairs and have confidence in its ability to provide requisite continuity to the brands I am associated with," Tendulkar said in a statement.
Tendulkar, who has scored a record 35 Test and 39 One-day centuries during a remarkable 16-year career, enjoys fanatical fan following in India and across the cricket world.
His 10,469 Test runs put him in fourth place behind West Indian captain Brian Lara and Australians Allan Border and Steve Waugh in the all-time scorers' list.
Tendulkar is also the world's leading One-day batsman, with 14,146 runs in 362 matches.
The recent dip in form - he averaged just over 20 in his last 11 Tests - and the spate of injuries raised fears Tendulkar's career may be coming to an end.
He was even jeered off the field in his home city of Mumbai in March after making one and 34 in the final Test against England which the tourists won to square the series 1-1.
However, many contemporary greats like Lara were not willing to write off Tendulkar. "Form is temporary, class is permanent," the 37-year-old Lara said recently.