Silas F. Fox was born in Josephsburg, AB, Canada on December 22, 1893. He was the youngest of three children born to attorney Caleb and Bessie Fox. Caleb died three weeks after Silas' birth. Silas' siblings were Paul and Florence. Bessie married again to a Mr. Roberts, postmaster and storekeeper. Robert's alcoholism caused the family great suffering and Bessie eventually had to leave him. Because of the family's poverty, Silas went to live with a Baptist preacher uncle.

He attended school from the age of four-and-a-half until 1904. When he was twelve, his family was reunited and moved to Toronto, where his sixteen year old brother Paul had a job working for the railroad. Silas began working as a riveter in a piano factory in 1905. He went on to jobs with other companies as errand boy and store clerk. At the age of nineteen, after being involved in church activities for many years, he gave his life to Christ. He now desired to go into Christian work. In 1915, he enrolled in the Toronto Bible College. While attending the school, Fox became acquainted with an English missionary from the Ceylon and India General Mission and was influenced by him to apply to that mission; he was accepted as one of their workers. Fox graduated from TBC on April 28, 1916, and on November 23 of the same year he married Emma Grau, his childhood sweetheart. Two days later the newlyweds left Toronto for Vancouver and from there they sailed to India, where they arrived in 1917.

For their first term, they were at first assigned to Hindupur, but the illness of another missionary caused them to be based in the town of Madakasira in West Madras. Much of their time was spent learning the Telugu language. Fox also visited some 300 villages around Madakasira, preaching to crowds in the village squares. One of his major co-workers was the Indian evangelist S. K. Agrippa. Toward the end of their first term, the couple went to Bangalore to recover after a serious bout of enteric fever. Around 1921, Fox started a little newspaper called Kalyandrug Sathyadootha, which translates as Kalyandrug Message of Truth. It was printed every month in the Telugu language and filled a need for Christian literature. It consisted of a sermon, anecdotes, questions and answers about Christianity, and notices of meetings. Fox continued for years to edit this paper, which was eventually renamed Kristava Nirikshina or Christian Hope. When the Foxes' first term ended in 1924, they returned to Canada on furlough.

Fox had begun to feel restricted by mission policy during his first term and this led, after discussion with mission leaders during his furlough, to his resignation in 1925, shortly after he had returned to India with his family. Thereafter he was an independent missionary who raised his own support. Fox continued to work in Telugu-speaking India. At various times he was based in Kuppam, Ootacamund, Anantapur, and Bangalore. In addition to editing the paper, he continued to evangelize and established harmonious relations with Brethren, Baptist, Mennonite, Lutheran, and Anglican missions. He was especially known for his willingness to use all kinds of flamboyant methods, from magic lantern slides to sandwich boards, to attract attention for the Gospel. In February of 1968, he left India for the last time and returned to Canada.

The Foxes had six children: Ruth Emma, Donald Silas, John Brainerd, Mary Anna, David Paul, and George Hudson.