Esure boss Stuart Vann is stepping down with immediate effect after 17 years with the group, in order to help the company "evolve its long-term strategy".
Until a replacement for Vann is found, the group's finance chief, Darren Ogden, will step in on an interim basis. He will be supported in the role by chairman Sir Peter Wood.
"On behalf of the board, I'd like to thank Stuart for his immense contribution to Esure," Wood said.
"Under his direction, the company has introduced a successful footprint expansion programme and the business remains on track to deliver three million in-force policies by 2020. We wish him all the best for the future. Looking to the future, the process of selecting a new chief executive is under way."
Vann said: "After 17 years at esure I feel now is the right moment to move on. I have enjoyed my time with the business immensely and am proud of all that we have achieved. I would like to thank the chairman and the board for their support over this time. Now is the right time to pass the baton on to someone else to take the business to the next level."
It was reported last year that Wood was hoping to sell Esure, and had pursued discussions with rival insurers.
Meanwhile, the group reported gross written premiums of £820m in 2017, up 25 per cent on the £655m posted in 2016.
Esure said it has "started 2018 positively and is trading in line with the board's expectations".