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.

Schools and businesses were shut and airport services suspended, as the cyclone made landfall with heavy rain and winds of up to 140km/h (85mph).
Teams from the army and National Disaster Relief Force, along with two naval ships, are on standby.
Fishermen in Andhra Pradesh and Tamil Nadu have been warned not to go to sea.
Police said disaster management teams had evacuated more than 15,000 people from low-lying areas.
The Tamil Nadu state government said in a statement that 260 trees in the city had fallen as a result of strong winds. Parts of the city have also been flooded.
Winds were so strong that glass panels were torn from the facade of Chennai's Hyatt-Regency hotel.
YK Reddy, director of the meteorology department in Hyderabad, told BBC Hindi the storm would weaken after making landfall.
The storm comes about a year after Chennai experienced devastating floods which killed 70 people.
In December 2011, more than 30 people died and many homes were damaged after a cyclone struck near the town of Pondicherry.
And in May 2010 at least 23 people died as a powerful cyclone caused widespread havoc across Andhra Pradesh.

RWE Npower is planning to bring down the remains of the boiler house at the Didcot A plant which partly collapsed in February, killing four men.
Three bodies are yet to be recovered.
The energy company said using remote-operated vehicles (ROVs) was preferable "since it limits the risk to life".
It called the conditions caused by the collapse "unprecedented at this scale in the UK".
A spokesman said the "traditional demolition method, which would require people to go underneath the structure to place demolition charges to bring down the building" would risk lives "because the building cannot be proven to be stable".
"The ROV option is the preferred route, with the traditional method being prepared as a back-up, should the robotic option not prove reliable."
Plans are being finalised and are due to be submitted to the Health and Safety Executive.
The spokesman added: "We understand that the time taken to recover the families' loved ones is deeply upsetting... our priority remains the recovery of the missing men and we are doing everything that is within our power to ensure it is progressed as fast and safely as possible."
Work to recover the men's bodies had been halted because contractors have reached a 50m (164 ft) exclusion zone.
In Oxfordshire County Council cabinet papers published earlier the cost to Oxfordshire Fire and Rescue Service of attending the incident and subsequent search and recovery operations stands at Â£300,000.
The length of time to recover Christopher Huxtable, 34, from Swansea, Ken Cresswell, 57, and John Shaw, 61, both from Rotherham, has previously been criticised by some family members.
John Howley, the uncle of Mr Cresswell, described it as "diabolical".
Labour MP for Rotherham Sarah Champion also branded it a "national scandal".
A man died and a 90-year-old woman was injured in a collision with a motorcycle on a busy road in Hastings.
[NEXT_CONCEPT]
At least seven people have been killed and thousands evacuated from coastal areas in two southern Indian states, as Cyclone Vardah lashed Chennai (Madras).
[NEXT_CONCEPT]
Robots should be used to place demolition charges at the base of the collapsed Didcot power station because using people "carries inherent risks to life", the site owner has said.