Earnshaw joined WTH UK in 2008 as product and commercial director and was promoted to managing director in 2018. She departs for personal reasons, but will support the business with its search for a new leader and support the transition.
WTH UK, which is owned by US firm World Travel Holdings, operates specialist cruise brands Cruise118.com, SixStarCruises and RiverVoyages in the UK market.
"I’ve been part of a huge success story at WTH UK," said Earnshaw. "[I] am very proud to have led the business for the past seven years, and of our many accomplishments, achievements and awards over the years since we started trading in 2008."
Earnshaw added: "I have been privileged to work with some exceptional people during my time at WTH and will be leaving the business in good hands with the strongest executive and management teams we’ve ever had. I have no doubt the business will continue to go from strength to strength."
Jeff Tolkin, co-chair and chief executive of WTH, said: "Alison’s exceptional leadership and impactful contributions over the past seven years have been key factors in the remarkable growth of our cruise business in the UK.
"I am confident in the leadership team she has built and grateful that she will be an integral part of the transition to a new managing director. We look forward to continued success in our UK division and wish Alison all the best."