The 77-year-old man, from Newhaven, and the woman, from Lewes, were on the A259 at White Rock when the accident happened on Thursday evening.
They and the motorcyclist were taken to the Conquest Hospital in Hastings, where the man later died.
Police said the 22-year-old motorcyclist, from St Leonards, and the woman were not detained.
Sussex police are appealing for witnesses to the accident, which happened just after 21:00 BST on Thursday.
A man died and a 90-year-old woman was injured in a collision with a motorcycle on a busy road in Hastings.