Watkin Lewes was educated at Shrewsbury school and Magdalene College , Cambridge , where he graduated in 1763 . He entered the Middle Temple and was called to the Bar in 1766 . He married well and his wife brought him considerable estates in Glamorgan and Pembrokeshire.
Having contested Worcester unsuccessfully in four elections, he sought civic and parliamentary honours in the City of London . His rise was rapid; in 1772 he was made Sheriff and also Alderman of Lime Street Ward , was knighted in 1773 , and in 1780 became Lord Mayor of London . In 1780 he was elected as one of the four Members of Parliament for the City of London , retaining this seat until 1796 . He remained an Alderman up to his death in 1821 and was High Bailiff of Southwark from 1784 to 1817.
He acquired the Plas Newyyd estate in 1779 and had a new house built to replace the orignal house on the site . He retained the name Plas Newydd meaning New Mansion.
The latter part of Sir Watkin's life was marked by financial difficulties. He was imprisoned for debt, and ended his days in the London Coffee House on Ludgate Hill within the rules of the Fleet Prison. It is suggested in Francis Jones's 'Historic Cardiganshire Houses and their Families' that he 'lost his money to fast women and slow horses'.
Sir Watkin Lewes's time at Plas Newyyd is beautfully described in Richards Fenton's 'Historical Tour Through Pembrokeshire" published in 1810 .....
"A little to the eastward of St Dogmaels, on a pleasant eminance stands Plas Newydd, new mansion, a name perfectly appropriate, being a late creation of my countryman and old friend Sir Watkin Lewes, as a temporary residence whenever he found leisure from city duties to visit his native country. It commands a most delightful view of the ruined abbey, the estuary of the Teivy and the town of Cardigan, a prospect pleasing to any eye ...."
In 1846 Plas Newydd was sold by auction along with 2 cottages and 25 acres to Captain George Bowen.