Sir Arthur Osmond Williams (17 March 1849 – 28 January 1927) was a Welsh Liberal Party politician.
He was born at Llanfihangel-y-Traethau, Merionethshire, Wales. He was the son of David Williams, M.P. for Merioneth 1868-1869, and Anne Louisa Loveday Williams. Arthur was educated at Eton. He married Frances Evelyn Greaves, daughter of John Whitehead Greaves and Ellen Stedman, on 3 August 1880 and had six children.
He was elected as M.P. for Merioneth at the 1900 general election and held the seat until 1910.