Pandy Llewenan was established as a carding, spinning and fulling mill around 1810, following the closure of the original mill at Pen Llywenan (to the E) at the end of the C18, which had been concerned with dyeing and fulling for at least 100 years previously. The contents of the original fulling mill at Pen Llywenan were valued and sold for £32 17s.3d. (£32.87) in 1782, including 3 spinning wheels, the press of the fulling mill and 2 fullers shears, among furniture and household goods. The present mill was built to replace the original pandy, and is recorded in a survey of the Presaddfed and Dronwy Estate (dated 1808), as the property of Sir John Bulkeley. The accompanying map shows the pandy as T-shaped in plan, with a mill pool to the E fed from the overflow from the corn-mill (Factory Llewenan) 300m NE. The pandy was run in conjunction with a smallholding of 17 acres (7ha). The inclusion of spinning within the factory was innovative on Anglesey; previously spinning and weaving was carried out at the home, and fulling only carried out at mills. Power looms were introduced to the mill in the 1890s, and new spinning machinery was installed in the former corn-mill (Factory Llewenan) c1900-5, after which time the pandy concentrated on weaving, fulling and dying. A steam engine was installed in the late C19, to power the machinery when water levels were low. In the early C20 the mill was producing woollen material for local use, particularly heavy protective clothing for farm workers. In 1940 the mill was bought by the present owner and began producing tweed for fashion garments and sports jackets, when it was known as the 'Anglesey Tweed Mill'. The mill was the last woollen mill to work on Anglesey, closing down in 1955, when it was recorded as having, amongst other items, 2 hand looms and a power loom (on the first floor), and a 120" ( 3m) warping mill and creel on the ground floor.
The mill range was built in 3 main phases; the original mill, at the S end of the range, is a 2 storey building, originally with hand-looms on the first floor. The original water wheel was on the S gable end; a second wheel was added to the N gable end, with a second building added to cover the wheel and provide more woking space for new machinery. A second extension was later added to the N gable end of the addition.