William Farel (1489 – September 13, 1565), Guilhem Farel or Guillaume Farel, is a French evangelist, and a founder of the Reformed Church in the cantons of Neuchâtel, Berne, Geneva, and Vaud in Switzerland.

He is most often remembered for having persuaded John Calvin to remain in Geneva in 1536, and for persuading him to return there in 1541, after their expulsion in 1538.

They influence the government of Geneva to the point that it becomes the "Protestant Rome", where Protestants tak refuge and non-Protestants are driven out.Together with Calvin, Farel worka to train missionary preachers who spread the Protestant cause to other countries, and especially to France.