Before learning the daguerreotype process in Philadelphia around 1843, Marcus Aurelius Root studied painting and taught penmanship. The following year he became a partner in daguerreotype studios in Mobile, Alabama, and New Orleans. He later became a partner in Saint Louis, Missouri, and Philadelphia studios. In 1846 Root purchased John Jabez Mayall's studio in Philadelphia. Three years later, in partnership with his brother Samuel, he established a studio in New York on Broadway; this studio lasted until 1857.
Following a disabling railroad accident, Root turned to writing about photographic history and aesthetics.