The land on which the hotel now stands, was originally part of the Jameson family estate (of Irish Whiskey fame) and the house itself was called St. Marnock's House.
King Edward VII often visited the Jamesons and on his last official visit in 1907 he unveiled a plaque which was designed specially for the occasion of the marriage between members of two great distilling families, Jameson and Haig. The plaque is still to be seen in what was the secret south garden.
The Jameson family had a nine-hole golf course on the site over 100 years ago; this golf course is now part of both the Portmarnock Golf Club and the Bernhard Langer designed Dublin Golf Links course.
Guglielmo Marconi, inventor of the wireless, was a son of Annie Jameson.
Portmarnock Beach with its wide sands witnessed the daring exploits of a number of pioneering aviators. James Mollison (husband of Amy Johnson) took off from Portmarnock Beach on the 18th August 1932 for what was acknowledged as the first solo east to west crossing of the Atlantic.