Paul Boissier, chief executive of the RNLI, has said he will retire next year after 10 years in the role.
The charity said in a statement that the former Royal Navy chief operating officer had confirmed "long-held plans" to step down next summer.
The statement said that under Boissier’s leadership the charity had maintained its place as one of the world’s foremost maritime rescue organisations while working hard to modernise and make itself more resilient in the face of an uncertain future.
Boissier said the job had been "challenging, humbling and heart-warming in equal measure" and it had been a privilege to be chief executive of "this brave, complicated and historic charity".
He said: "In an uncertain world, we have continued to provide an outstanding service to the public, while modernising the organisation itself and strengthening the RNLI for any challenges that might lie ahead."
Stuart Popham, chair of the RNLI, said: "The RNLI is one of UK’s longest-established charities and its leader has a uniquely challenging job: providing both a modern emergency service and running one of the UK’s most valued and respected volunteer-led charities.
"Paul has worked hard to modernise the RNLI over the past 10 years and I am now looking for a new leader for the RNLI to build on his legacy."
The charity said it would place an advertisement on its website for a successor to Boissier from Sunday.