While his novel - for which he already has a deal - will be his most immediate project, Howarth will also be looking to explore other ventures within publishing.
"Various things have cropped up," Howarth said. "I thought I'd leave and try and pursue other things before I get so old and bedded into the job that I can't take that kind of risk."
However, NatMags is keen to keep him attached to the magazine in a consultancy role. Howarth said: "The strategy is to keep the magazine edging away from what the pack of men's magazines are doing. There are discussions about some kind of executive role for me to make sure that carries on."
Howarth worked in the fashion industry before spending four years at GQ and two years at Arena. Three years ago he initiated a repositioning of the magazine in a bid to present itself as a thinking-man's title.
Duncan Edwards, the managing director of NatMags, said: "We are very sorry to see him go, but are pleased that he will be with us for another three months, and have every confidence that his association with Esquire will continue."