Fox was born in Ireland. His father, who died before Fox was ten, was a physician and member of Parliament. Fox attended Stamford Hill Jesuit college near London, and became an electrical engineer. However, he early discovered that he had healing power, and from the time of his late teens studied New Thought. He came to know the prominent New Thought writer Thomas Troward.

Fox attended the London meeting at which the International New Thought Alliance was organized in 1914. He gave his first New Thought talk in Mortimer Hall in London in 1928. Soon he went to the United States, and in 1931 was selected to become the successor to James Murray as the minister of New York's Divine Science Church of the Healing Christ. Fox became immensely popular, and spoke to large church audiences during the Depression, holding weekly services for up to 5,500 people at the New York Hippodrome until 1938 and subsequently at Carnegie Hall. He was ordained in the Divine Science branch of New Thought.

Fox's secretary was the mother of one of the men who worked with Alcoholics Anonymous co-founder Bill W., and partly as a result of this connection early AA groups often went to hear Fox. His writing, especially "The Sermon on the Mount," became popular in AA.

Contemporaneous New Thought writers include Ernest Holmes, Thomas Troward, Emma Curtis Hopkins, H. Emilie Cady, Malinda Cramer, Charles Fillmore, Myrtle Fillmore, Joel S. Goldsmith, James Dillet Freeman, Eric Butterworth, Florence Scovel Shinn.