Engineer and leading railway contractor. Born in Houston (Renfrewshire), the son of a spinner. He started work in a cotton mill at the age of only 9, but by 1863 had joined a company of bridge manufacturers in Glasgow. By 1872 he had his own business, the Dalmarnock Iron Works in the east end of the city.
Arrol was the contractor responsible for building the Forth Rail Bridge (1890) and the replacement Tay Rail Bridge (1887) which were the two most substantial bridges in the world of their time and remain in constant use today. He was also responsible for Tower Bridge in London (1894), bridges over the Nile at Cairo (1908) and multi-span bridges over the River Clyde at Bothwell and the River South Esk at Montrose. His company also built the Bankside Power Station in London, which now forms the Tate Modern Art Gallery.
He had a reputation for being ingenious and energetic. He was knighted in 1890 and was elected the Liberal Member of Parliament for South Ayrshire, serving between 1892 and 1906.
Arrol bought an estate at Seafield, near Ayr (1885), and built a house there, where he lived until his death.