Casasola began his career as a typographer for the newspaper El Imparcial, eventually moving to reporter then on to photographer in the early 1900s. He became a photographer in 1894. By 1911 Casasola was credited with founding the first Mexican press agency, Agencia Fotografica Mexicana. Casasola was later thanked by the interim president in 1911, Francisco León de la Barra, for having "inaugurated a new phase of freedom in the press photography." By the end of 1912 the agency had expanded and changed its name to Agencia Mexicana de Informacion Fotografica. The agency brought on more photographers and began purchasing pictures from foreign agencies and amateurs, then redistributing those photographs to newspapers.
When El Imparcial went out of business in 1917, Casasola recovered the newspaper's archives, eventually compiling many of the photographs into the famed "Album histórico gráfico" which covered the events of the Mexican Revolution. Casasola only managed to print the first 6 volumes covering the years 1910 to 1912. It is believed the work did not fare well due to the changing attitude of people wanting to move on from the death and suffering that plagued the civil war.
In 1920, Casasola as well as other notable Mexican photographers founded the Mexican Association of Press photographers.
Casasola's collection was later dubbed the Casasola Archive where it was later housed at the National Institute of Anthropology and History of Mexico, the collection totaling over 500,000 prints and negatives.