New Delhi, Sept. 10 -- A surprise U-turn by private equity giant Advent International prompted O.P. Bhatt to resign as chairman of Coforge Ltd on Tuesday, as a 'no' vote by its largest shareholder denied the veteran banker the minimum 75% vote required for an extension.

Advent's vote came just three weeks after a panel including its nominee signed off on an extension, against the backdrop of differences on the company board on Bhatt continuing at the helm of India's fastest-growing IT services company.

The flip-flop by a private equity giant in India's $315 billion IT outsourcing industry marks a rare case of a minority investor using its voting power to block a chairman's reappointment. The news of the resignation, disclosed by the com...