With the banking hall in High Street decked out in balloons, the branch's former manager Arwel Davies was invited to cut the specially-made celebration cake, complete with NatWest logo.
The branch first opened in 1836, by the recently-founded National Provincial Bank of England. Pwllheli's coastal location, with its shipbuilding and fishing industries, attracted the attention of the bank's directors, who agreed that the town would serve as a suitable location for their next branch. Little is known about the branch's early years, but by 1844 it was trading from a building in Traeth Street, under manager Charles Archibald. By 1859 the business had relocated to Caroline Square, and by 1880 it had moved again, to its current premises at 34, High Street.
In the 1890s, Pwllheli was redeveloped by the entrepreneur Solomon Andrews, a Cardiff businessman. New houses and roads were built, and a promenade was erected. Andrews also oversaw the construction of the town's tram network. While the town was undergoing this transformation, National Provincial Bank decided that it needed larger accommodation so the branch was extensively refurbished and extended, with work completed by1898.
By the start of the 20th Century, banks faced increasing competition and were forced to grow in order to remain competitive. In 1918, National Provincial Bank of England merged with Union of London & Smith's Bank to form one of the emerging 'big five' High Street banks. The new bank traded through more than 700 local offices, and in 1924, following a series of acquisitions, the bank's name was shortened to National Provincial Bank.
The tram system established by Solomon Andrews ceased operating in 1927, when some of the tracks were damaged during a storm.
In 1968 National Provincial Bank and Westminster Bank, along with National Provincial's subsidiary District Bank, announced their intention to merge. All three banks were combined over the following 18 months, trading as National Westminster Bank from 1 January 1970.
Branch manager Beryl Worsley said: "Thank you so much to Mr Davies for joining us to cut the cake, and to our customers for helping us to mark the occasion. As a bank we are always keen to look forward, making sure we move with the times to give our customers what they want.
"That said, it's also important to mark these milestones that remind us how long we've been providing a service to our local community. Between us, we have over 180 years' banking experience at this branch!"