William Alexander McArthur (1857 – 7 June 1923), was a British Liberal politician and businessman.

McArthur was born in Sydney, Colony of New South Wales, the eldest son of Alexander McArthur^[1] and his wife Maria Bowden, the second daughter of the Rev. William B. Boyce.^[1][2] McArthur's father was a businessman and politician in Australia and England, becoming MP for Leicester.^[3] McArthur was educated privately.

On 12 August 1890 at the Trinity Wesleyan Church, Abingdon-on-Thames, Berkshire, he married Florence Creemer (died 24 October 1940),^[4] the third daughter of John Creemer Clarke of Wayste Court, Abingdon, and the couple had one son and two daughters.^[5][6][7]

He worked as a merchant like his father,^[3] and became a partner in the firm of W. and A. McArthur, Colonial Merchants. He was a Director of the Bank of Australasia.^[1] He was Mas Commr. for New South Wales at the Colonial and Indian Exhibition in 1886.^[5]

McArthur was elected to Parliament for Buckrose at the 1886 general election, with a majority of a single vote, but was unseated on a scrutiny being held and the seat was awarded to the Conservative candidate, Christopher Sykes. He entered Parliament for St Austell in an 1887 by-election, a seat he held until 1908. McArthur served in the Liberal administrations of William Ewart Gladstone and the Earl of Rosebery as a Junior Lord of the Treasury from 1892 to 1895.

McArthur died on 7 June 1923 at a private hospital in Sydney, aged 66, and was interred 8 June at South Head Cemetery.^[7]