The ceremony was attended by around 500 people
A minute's silence has been held to mark the unveiling of a memorial carrying the names of 778 RNLI lifesavers who died at sea.
It took place at 1220 BST as the Duke of Kent uncovered a boat sculpture at the charity's headquarters in Poole, Dorset, dedicated to the lost rescuers.
Around 500 people, including relatives, friends and colleagues of those commemorated also attended.
RNLI stations across the UK and Ireland flew the RNLI flag at half-mast.
The Duke of Kent - who has been RNLI president for 40 years - said the day was one of "celebration and commemoration".
He said the charity had saved over 137,000 lives since its foundation in 1824 and its lifeboats currently launched more than 8,000 times a year.
"Saving life at sea is inescapably a dangerous business," he added.
"In these times we are asking more of our lifeboat crews and our lifeguards than ever before."
The RNLI Memorial stands at more than 4.5m (15ft) in height and has been designed by Sam Holland ARBS.
It carries the family motto of the RNLI's founder, Sir William Hillary: "With courage, nothing is impossible."
The sculpture depicts a figure in a boat saving another from the water.
The RNLI has invited members of the public to pay their respects too by adding a tribute on the RNLI online book of commemoration.
RNLI chief executive Andrew Freemantle said: "The RNLI memorial is a tribute to the many hundreds of people who have given their lives selflessly to save others over the last two hundred years and it will ensure that the sacrifices made by our volunteers, and others, while saving lives at sea are never forgotten.
The sculpture depicts a figure in a boat saving another from the water
"Its location, in front of the Lifeboat College in Poole, is truly fitting and will inspire generations of lifesavers from all over the British isles who will train here in the years to come."
Among those present was Thomas Cocking, who saw on the memorial the names of his great-grandfather, also called Thomas Cocking, and great uncles John B Cocking and Richard Stevens.
Mr Cocking, 53, who serves as coxswain mechanic of the St Ives lifeboat, said: "There are thousands of people throughout the country who support it so to acknowledge them today is a very important part of the RNLI's history.
"It's important for the volunteers who gave their lives."
Among the RNLI stations which observed the minute's silence was the boat house on Howth Pier, Dublin.
The charity operates 43 lifeboat stations on both sides of the Irish border.