WE's retainer began on 1 May, after winning the brief in a pitch process that began in January.
Red Consultancy had previously worked with Capgemini for more than a decade, and previously held the UK-retained brief. Mike Morgan, CEO of Red, said: "We are very proud of our decade of partnership with Capgemini."
The brief, which makes Capgemini one of the largest UK clients of the Seattle-headquartered agency, covers day-to-day media relations and content creation, as well as work on its cross-year campaign with online retail industry association IMRG, with whom it publishes a monthly e-retail sales index.
Capgemini provides services for UK blue-chip companies and public bodies including Nationwide, National Grid, the Environment Agency and Anglian Water. It has also worked with HMRC and the police. Capgemini has about 9,000 staff in the UK, and a total of 190,000 employees across 40 markets globally.
"WE Communications demonstrated a hunger for our business and a strong understanding of our target audience in the UK. Beyond that, we believe it is the agency that will most challenge our thinking, enabling us to continue to evolve and succeed with our communications programme," Magda Bulska, UK PR manager at Capgemini, said.
Marcus Sorour, UK MD of WE, told PRWeek: "WE is growing again and this is part of that." He said the agency would unveil more client news in the coming weeks.
The Global Agency Business Report shows that WE posted 3 per cent global revenue growth in 2016, reaching $101.8m (£78.8m), making it the world's 22nd largest PR firm.