William Murdoch (sometimes spelled Murdock) (August 21, 1754 – November 15, 1839) is a Scottish engineer and inventor.

Murdoch is employed by the firm of Boulton & Watt and works for them in Cornwall, as a steam engine erector for ten years, spending most of the rest of his life in Birmingham, England.

Murdoch is the inventor of the oscillating cylinder steam engine, and gas lighting is attributed to him in the early 1790s, also the term "gasometer".

However, Archibald Cochrane, ninth Earl of Dundonald, had already in 1789 used gas for lighting his family estate.

Murdoch also makes innovations to the steam engine, including the sun and planet gear and D slide valve.

He invents the steam gun and the pneumatic tube message system, and works on one of the first British paddle steamers to cross the English Channel.

Murdoch builds a prototype steam locomotive in 1784 and makes a number of discoveries in chemistry.

Murdoch remains an employee and later a partner of Boulton & Watt until the 1830s, and his reputation as an inventor has been obscured by the reputations of Boulton and Watt and the firm they founded.