Blue Rubicon will support British Gas' corporate and consumer reputation after emerging through a competitive pitch process started earlier this year.
The agency will explain the company's new simplified tariffs and metering technology to consumers, as well as the benefits British Gas brings to the British economy.
Fiona Joyce, partner at Blue Rubicon, noted that the firm employs 30,000 people in the UK and is investing significantly in technology to keep energy affordable and ensure the security of the UK's energy supply.
Despite a measure of downwards pressure on fees, the brief is thought to be worth a significant six-figure sum and is one of Blue Rubicon's largest accounts.
Joyce will lead the account with Fraser Hardie, senior partner, and Chris Norton, MD. The agency will report to Paul Fincham, external comms director for British Gas.
Blue Rubicon first won British Gas' retained comms account in 2007.