[1] William was born in 1722 in Luncarty just north of Perth, Scotland the fifth child of David Sandeman and his second wife Margaret Ramsay.
As part of his Glasite obligations, he journeyed with his brother Robert in the first attempt to form a London Sandemanian congregation in 1761.
In the early 1760s, William Sandeman opened two further linen centres: Milntown (now Milton) in Easter Ross and Fortrose on the Black Isle near Inverness.
In November 1784, Sandeman visited Lancashire cotton mills and Richard Arkwright the inventor who had pioneered cotton-spinning machinery in Derbyshire.
Sandeman, Arkwright and others established the Tay River–powered cotton mill in Stanley (just north of Luncarty, Perthshire) in 1786/7 with 3200 spindles.