The digital agency will now work on a variety of projects with a focus on online brand awareness, eCRM, customer recruitment and driving traffic to the npower website.
The agency triumphed in a competitive pitch called by npower's parent company, RWE, in April as part of an overhaul of its online marketing strategy.
Last year, the utility company appointed the Aegis-owned digital media specialist Diffiniti to develop an online media plan to help the brand compete with British Gas.
It later announced its intention to double its marketing spend to £20 million, promising to increase the proportion of its budget spent online from 7 per cent to 14 per cent. At the same time, it bolstered its marketing department by appointing a number of digital marketing specialists.
Npower denied it had made an appointment, while Grand Union declined to comment.