William Metcalfe is best known for his promotion of vegetarianism in the US. He was one of the main organizers, with William Alcott, Sylvester Graham, and Russell Trall, of the American Vegetarian Society,  in 1850 and became President in 1859, succeeding Alcott. He was born in England, in Orton, Westmoreland, on 11 March 1788. Converting to, and becoming a minister of, the Bible Christian Church in 1811, he moved to the US and founded the Philadelphia Bible Christian Church in 1817. This was the first vegetarian church in the US and among its more controversial tenets was the belief that Jesus Christ was vegetarian.

Metcalfe is explicit in his admonishment not to kill and eat animals for their own sakes, to respect the lives given to them by God and to respect the humanity given to humankind by God, which is hardened by violently slaughtering animals. Metcalfe links vegetarianism to other social justice issues such as pacifism, Temperance, and Abolition. He died in Piladelphia on 16 October 1862.