Mario R. Sonsini was the son of Mr. and Mrs. Pasquale Sonsini who lived in Coatesville, Pennsylvania. Mario was one of three children.
Mario attended local schools, and worked at Lukens Steel Company.
Mario joined the Marine Corps July 20, 1941. He served in the Pacific theater of operations.
His parents received a telegram from General A. A. Vandergrift of the Marine Corps. Private First Class Mario R. Sonsini was Killed In Action on October 25, 1944 in the Central Pacific area. This may have been on Leyte Island, the most prominent combat action on that date by both the Army and Marines.
A Military mass was held at Our Lady of the Rosary Catholic Church on November 11, 1944.
His brother James served in the Navy during the war.