Joseph Birren (1864-1933) was a commercial artist who became President of the P&C in 1903 and eventually closed his shop in 1916 to pursue fine art full time. Like several other P&C artists, he later specialized in landscapes of southern California.
One source claims that he had a one-man show at the Art Institute in 1916, but the museum's website makes no mention of it. Instead, he was probably included in the the 20th Anniversary P&C exhibit which was held that year. He later appeared in a 4-man show at the museum in 1924.
Earlier in his career, he specialized in painting cycloramas, including one of Gettysburg. (but I'm not sure if he worked on the one in the national monument). This kind of work took him to Europe and Australia.
His son, Birren, specialized in color theory, as it might be applied to industrial design as well as painting hospitals and factories.