After 1825, William Middleton was listed as a merchant, factor, and table knife manufacturer in George Street. He may originally have partnered John Woollen. By 1837, he lived in Stand House, Fulwood Road. His son, also named William, had joined the business by that date. He was a merchant in Union Street, with a residence in Broomhall Place. By 1839, father and son had formed Middleton, Newton & Middleton, which had a New York office in Maiden Lane. The ‘Newton’ was Francis Newton – an individual who is unidentified but may have been Francis Newton. On 14 August 1841 William Middleton Sen. died at Stand House, aged 51, and was buried in Ecclesall. In the following year, the partnership was dissolved.