The works near The Chandlery will see the existing 36-bay car park almost double in size to provide 68 spaces including six disabled bays.
The works will involve building over the existing neighbouring scrubland with asphalt, new drainage and refurbishment of a section of wall between the upper and lower car parks which will be partially dismantled and rebuilt.
New low railings will also be fitted around the new perimeter, leaving the existing coastal path intact.
Sea fret - a look at the foggy phenomenon which spoils sunny days in Northumberland
Police seize large drugs haul in north Northumberland
Crossing closure will make railway line like the 'Berlin Wall' claims Blyth resident
Six people and a dog rescued from stranded vehicles on Holy Island causeway
Ashington FC to release new Ireland-inspired away kit in tribute to Jack Charlton
The works are set to start on September 13 and are due to take around 14 weeks.
During this time, sections of the existing upper and lower car parks will be unavailable to allow for construction.
Limited nearby parking along the quay walls will still be available and other alternative car parks in Berwick will remain available.
Cllr John Riddle, cabinet member for local services at Northumberland County Council, said: “Creating extra parking in all our towns can be a challenge but it’s great to be starting this major expansion of this quayside carpark.
“We will be working to keep disruption to a minimum and this is why we avoided starting the scheme during the summer holidays when parking was already at a premium due to the large visitor numbers.”
Cllr Catherine Seymour, member for Berwick North, added: “With increasing visitors to our historic town in recent years, the extra car spaces will help with the acute shortage of parking throughout.“This will benefit the public, traders, culture, arts and accommodation sector and improve the economy of Berwick.”
Planning permission for the scheme was granted in August 2019.
The proposal split Berwick Town Council’s planning committee at the time, with some voicing concerns about the visual impact on a prime riverside location, although others said there was a need for more town centre parking.
In 2017, a council commissioned parking study of Berwick town centre recommended that 50 more parking spaces were needed as soon as possible, with 185 needed by 2020 and 260 by 2030.
The site is still being marketed as a development opportunity.