The latest deal, for £350m over five years, is for a system and processes transformation programme.
This is the third multi-million pound deal in 18 months that Tech Mahindra has won from BT Group and brings its total BT-related business to more than £1bn.
In December 2006 it won a £500m contract from BT Global Services. Earlier this year, it won a £175m deal from BT for application support.
BT Global Services is expected to announce in August details of a further contract, this time for the £5bn worth of IT contracts it manages on behalf of network clients.
C P Gurnani, president of international operations at Tech Mahindra, said despite the large wins from BT, its revenue from the company during the quarter dropped to 62% from 64% of its total. This was because its non-BT revenues grew 14%, he said.
Tech Mahindra, India's sixth-largest software exporter, reported total revenues of £468m for the year ended March 31, 2008. For the first quarter this year it reported net profit after tax of £32m on sales of £136m. Telecom Fiji and Telecom New Zealand are among recent signings.