Esnouf has been at the company for more than six years, having previously spent more than five years as corporate and internal comms head at German energy supplier E.ON.
E.ON acquired Npower in September last year as part of a €43bn asset swap with fellow German energy giant RWE, and is reportedly making thousands of roles redundant as it shuts down Npower sites.
Esnouf said leaving Npower after six-and-a-half years "will be strange".
"Checking energy industry press cuttings at 6.30am, and the cut and thrust of energy retail, have become a way of life," he said. "It’s been a hugely enjoyable time – even though one year The Independent said I had the second-toughest comms task in Britain."
Esnouf said two things stood out about the challenges of his role.
"First, keeping our people engaged through real change – 4,000 fewer roles, a failed merger and now a takeover. This was done through a strategy of building trust through transparency, led by head of internal comms Johnathan Jones and Judy Wood," he explained.
"And second, finding creative ways to build our reputation – through our Fuel Bank project in particular, with the work led by head of PR Zoe Melarkey and then Sunita Patel. But with Npower being taken over by E.ON, all good things come to an end in April, and now I need to figure out what I want to do next."
E.ON is folding Npower's domestic and small-business customers into its existing British business.
In November last year, it was reported Npower could cut up to 4,500 jobs as part of a shake-up by its new owner that will include the closure of most of its UK sites.
The process will cost £500m which is set to be carried out over the next two years.