South Stack Rock lies separated from Holyhead Island by 30 metres of turbulent sea, surging to and fro in continuous motion. The coastline from the breakwater and around the south western shore is made of large granite cliffs rising sheer from the sea to 60 metres.
South Stack Lighthouse was first envisaged in 1665 when a petition for a patent to erect the lighthouse was presented to Charles II. The patent was not granted and it was not until 9 February 1809 that the first light appeared to mark the rock. The lighthouse was designed by Trinity House surveyor Daniel Alexander and originally fitted with Argand oil lamps and reflectors. Around 1840 a railway was installed by means of which a lantern with a subsidiary light could be lowered down the cliff to sea level when fog obscured the main light.
On 25 October 1859 it is said that the most severe storm of the century occurred, known as the 'Royal Charter' gale; and on that and the following day over 200 vessels were either driven ashore or totally wrecked with the loss of 800 lives.The steamship Royal Charter was among these, sinking within yards of help with the loss of almost 500 passengers and crew.
In the mid 1870s the lantern and lighting apparatus was replaced by a new lantern. In 1909 an early form of incandescent light was installed and in 1927 this was replaced by a more modern form of incandescent mantle burner. The station was electrified in 1938.
On 12 September 1984 the lighthouse was automated and the keepers withdrawn. The lighthouse is now monitored and controlled from Trinity House’s Planning Centre in Harwich, Essex.