William Munnings Arnold (10 October 1819 – 1 March 1875) was an Australian politician, a member of the New South Wales Legislative Assembly from 1856 until his death.

Arnold was born in the village of Ellough in Suffolk, England and was the son of an Anglican clergyman.

Arnold migrated to Australia in 1839 and made a substantial fortune from investments in the pastoral industry and gold trading.

He invested in a number of large properties on the Paterson River in which he drowned during major flooding in 1875.

He was noted for his objectivity and fairness as speaker and his decisions were rarely questioned by either the government or opposition.