WNS Assistance has won the contract to manage the entire BT motor fleet.
The fleet was formerly managed by Aon Motor Accident Management (AMAM), which was acquired by Nobilas International in June.
The BT fleet consists of 45,000 vehicles for both management and sales staff, the majority of which are vans.
WNS (formerly Town & Country) said the deal included uninsured loss recovery, third party claims handling and access to its accident management programme.
BT Fleet general manager Janet Entwistle said: "We are confident that all our claims will be handled within the tightest possible timescales."
Nobilas International director of operations Jeff Bullen said the loss didn't deter him from buying the company.