Engine’s creative agency WCRS and customer engagement agency Partners Andrews Aldridge will lead the account, with support from other agencies in the group.
The agencies will be responsible for delivering integrated marketing activity that helps E.ON better engage with its customers.
Engine secured the business following a review process run by ISBA that kicked off in January, when E.ON decided to consolidate its UK creative and CRM accounts.
The final stage was between Engine and Karmarama. A partnership between Mother and the CRM incumbent Helia was knocked out at an earlier stage.
DLKW Lowe was the incumbent on the creative account, but decided not to repitch.
E.ON’s B2B and marketing director, Anthony Ainsworth, said: "[The appointment] marks a significant shift in the way we’re responding to an increasingly fragmented media landscape, having one agency that spans our above- and below-the line activities allows us to take a truly holistic and channel-neutral approach to engaging with our customers."
He said Engine stood out because it demonstrated a keen desire to improve the experience of customers and offered a "talented team of experts who can help us better integrate our activities across the whole marketing mix."
"This was a challenging brief and we believe that, by working with Engine, we can build on the significant improvements we’re already making for the benefit of our customers as we work to become their trusted energy partner," he added.
Engine UK’s chief executive, Debbie Klein, said: "E.ON is an ambitious and forward-thinking client. We’re excited to extend our relationship with them to help engage with customers in new and innovative ways."
Engine will start work on E.ON’s through-the-line activities from May 2015.