In 1869 Cassidy was born in Covington, Kentucky and named Ira Dymond Gerald Cassidy. He studied art at the Institute of Mechanical Arts, under Frank Duveneck, and continued his studies at the Art Students League in New York.
Cassidy was stricken with severe pneumonia in 1890. He was only 27 years old and at the onset of gaining recognition as an artist. He moved to Albuquerque, New Mexico, where he was placed into a sanitarium to regain his health, which he did. The move to New Mexico was pivotal as it provided Cassidy with his first exposure to the American Southwest, the people and the landscape. He painted this genre, and became well known for it, his entire career.
1916 - Graend Prize for Murals, Panama-California International Expo, San Diego, CA
1921 - Kanst Gallery, Los Angeles, CA
1928 - Pasadena Art Institute, Pasadena, CA
1928 - LACMA, Los Angeles, CA
1929 - Stendahl Gallery, Los Angeles, CA
Indian Arts Building San Diego, CA
Bancroft Library, UC Berkeley, Berkeley, CA
San Diego Museum, San Diego, CA
University of New Mexico, Albuquerque, NM