Manley Marcus Gillam was born April 15, 1846, in Alba, Bradford County, Pennsylvania. He was raised on grain and dairy farm in rural Pennsylvania. He married Alice Maria Goodell in 1872 in New Jersey. The couple appear to have had eight children. In 1862, Gillam went to Washington, D.C. where he was on duty with the Quartermaster's Department of the U.S. Army for two years, during the Civil War. He subsequently studied business and became a bookkeeper. He worked briefly as a stenographer for the Pinkerton Detective Agency in Philadelphia, then entered into the field of journalism. He joined the staff of the Boston Post in 1872 and became city editor in 1873, a post he held until 1879. He was a member of the editorial staff of the Philadelphia Record starting in 1879 and became managing editor that same year, holding this position until late 1886. He then became advertising manager for the large retail business of John Wanamaker of Philadelphia.

It was during his time as advertising manager with the John Wanamaker Department Store that Gillam was in contact with developers of Eddy (later Carlsbad), New Mexico and the Pecos Irrigation and Improvement Company. It's not know how that relationship was established but Gillam apparently owned some land in the Pecos Valley of New Mexico.

Gillam resigned from the Wanamaker firm in 1895 to take a similar position with Hilton, Hughes and Company in New York City. He remained in New York the rest of his life, working in the advertising industry. He died in Flushing, New York, March 24, 1925.