Immigrating to New York at three years of age, by 1850 Mallon was establishing himself in the Savannah, Georgia area as teacher in private schools and, in 1854, establishing a public school. Mallon returned to New England in 1855 for studies at Brown University.

Returning to Savannah with his bride, Mallon opened the Massie School in 1856 and was named superintendent of the city’s schools a decade later.

He served in the Atlanta area as a soldier in 1864 during the American Civil War.

Mallon was elected Superintendent of the Atlanta Public Schools in 1871 and served in that role until resigning in 1879. In Atlanta, Mallon became a much respected educator by fellow teachers and students and brought much attention and notoriety to both the school system and his practices. Having long declined offers for relocating, Mallon finally relented to take the position of principal at Sam Houston Normal Institute. SHNI officially opened on October 10 – Mallon died eleven days later, October 21.

The Mallon House was named in his honor.