Based in the US and listed on the New York Stock Exchange, Worldcom is the seventh largest company in the world and made sales of more than £15bn last year.
WorldCom appointed Lewis this week after an eight-way pitch at the end of last month.
Work starts this week and will be overseen by the agency's director of international accounts Kath Pooley.
The brief is primarily focused on the UK, with
Lewis reporting to head of corporate communications Richard Woods.
He said: 'What we need is a significant PR footprint in the internet and technology space -- we are already well known
as a telecoms company.'
Lewis's account is also thought likely to include work across the agency's network
of offices -- including Munich, Sydney, San Diego and Boston.
The brief will includes some PA work and a tech industry analyst relations programme, as well as corporate tech PR plans.
The pitch list included Hotwire PR, and Harvard PR as well as the incumbent Porter Novelli Convergence Group, which was hired
in April of this year to integrate WorldCom's PR efforts following a string of acquisitions.
In the US the company will continue to use the Merritt Group for PR advice, reporting to that country's head of comms Claire Hassett.
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