BT plans to extend its enterprise services offering in the US with the acquisition of International Network Services.
The California-based company's services include information risk management and infrastructure transformation, and consulting on business productivity and on enterprise architecture and governance.
The acquisition will add 900 staff to the 7,000 already working in BT's global professional services units.
INS will become a wholly owned subsidiary of BT, part of its Global Services division, as a result of the acquisition. Its chief executive, David Butze, will report jointly to Chuck Pol, president of BT Americas, and to Gary Bullard, president of BT Global Business and Services.
BT will pay just over £100m for the company, and expects the deal to close in a few weeks, a spokesman said.
In October, BT bought another California company, US consultancy Counterpane Internet Security for a price it said was in the "tens of millions of dollars”. Counterpane, with a staff of 75, monitors and protects the networks of around 550 companies.