The agency is working on an ad campaign for the brand to come out this year as well as developing its communications strategy.
Good Energy is prioritising the addition of business customers, having concluded that competition is intense in the consumer energy supply business. It is also enhancing its services for customers who generate their own energy, for example from solar panels, to sell back to the grid.
Interim marketing director Paul Tavener said: "This is a really important time for us as we move towards being a brand that is not just an energy provider. Creature felt like a great fit for us all along and we’re excited to partner with them for the next phase of our journey."
Tavener replaced Hannah Darby, who left in May.
Dan Cullen-Shute, chief executive of Creature, added: "Since we set Creature up, we've always talked unashamedly about wanting to be a Good agency, as well as a great one; and in Good Energy, we may have found the perfect partners for doing just that. The energy sector is ripe for a spot of intelligent misbehaviour, and we're dead chuffed that we've got the chance to supply it with the good guys."
Creature’s appointment comes after Good Energy appointed Fetch as its mobile agency.
Good Energy has previously worked with Lucky Generals, which it appointed in 2013, but it has recently been out-marketed by newer energy start-ups such as Ovo and Bulb.
Ovo, which recently passed 850,000 customers, recently unveiled new TV advertising created by Uncommon, while Bulb, which recently passed 300,000 customers, has achieved 30% of its sign-ups through its offer of £50 referral credit for both referrer and new customer.
Bulb recently ran its first TV advertising but it was restricted to the area around Brighton and was created in-house, according to a blog by head of growth Jenny Zhao (formerly of Manning Gottlieb OMD).