The companies will create Capgemini Energy Limited Partnership to provide services initially to TXU, with a plan to offer similar services to other energy companies in the future.
Other outsourcing suppliers last week announced a slew of new deals, partnerships and contract extensions.
Motor insurer Cox has signed a £138m, 10-year contract with CGI Group Europe to manage all aspects of the insurer's IT infrastructure. More than 200 Cox staff will transfer to CGI.
Suffolk County Council, Mid-Suffolk District Council and BT have signed a 10-year, £380m partnership to create an IT services joint venture. BT will invest £50m over the course of the contract in systems and infrastructure. Suffolk County Council will invest £30m a year and the smaller government body will pay £3m a year.
BT has also signed a £40m deal with recruitment agency Manpower to roll out a global network and telecoms infrastructure.
Computer Sciences Corporation has signed contracts worth a total of £62m with Whitbread, Allders Department Stores, DIY retailer Homebase and tobacco company Gallaher.