William Gray Purcell was born in Wilmette, Illinois in 1880. He was raised by his grandfather, William Cunningham Gray, editor of "The Interior", a religous magazine, on the same street that Frank Lloyd Wright would later build his first home on. Purcell graduated from Oak Park and River Forest High School in 1899 and went on to graduate from Cornell University in 1903 with a degree in architecture. It was at Cornell University that he met his future partner George Feick Jr. He then returned to Chicago and obtained work with Louis Sullivan for five months. While he was there he met another of his future partners, George Grant Elmslie

With work on the decline in Sullivan’s office, Purcell left for Los Angeles to visit Myron Hunt and Elmer Grey and then on to San Francisco where he worked for John Galen Howard. He left San Francisco for Seattle and the firm of Charles H. Bebb and Leonard L. Mendel in 1905. In 1906 he returned to Oak Park for a short stay and shortly thereafter left for Europe and Asia with former college classmate George Feick Jr.

Upon their return to the United States in 1907, Purcell and Feick established their partnership in Minneapolis, Minnesota. The firm was known for designing churches, residences and various types of civic and commercial buildings throughout California, Connecticut, Massachusetts and the Midwest. They received their first bank commission in 1907, the unrealized First National Bank in Winona, Minnesota. Their design for the bank, which was derived from Wright’s Unity Temple, was rejected for a more classical design. It was not until 1911 that Purcell, Feick & Elmslie (who had joined the firm in 1909) got their chance to execute a bank in Winnona, the Merchants Bank Of Winona. Over the course of a decade the firm had executed over 70 buildings along with numerous other unrealized designs, making them the most productive of the Prairie School architects.

In 1913 George Feick Jr. left the firm, while Purcell and Elmslie continued their partnership officially until 1922. The new partnership of Purcell and Elmslie produced numerous banks across the Midwest as well as the Woodbury County Courthouse in Sioux City, Iowa in collaboration with former Sullivan protégé William L. Steele.

During World War I he moved to Philadelphia to take a position as advertising manager for a local Philadelphia firm, but then returned to Minneapolis in 1919, as the company entered into bankruptcy. In 1920 Purcell went into semi-retirement because of failing health and moved to Portland, Oregon. In Portland he became the director of the Architects’ Small House Service Bureau and an editorial assistant for Northwest Architect magazine. Purcell moved to Pasadena, California at the end of the decade and ultimately retired there. He continued to write until his death on April 11, 1965. He was buried in the Forest Home Cemetery in Forest Park, Illinois under the monument that he designed while a student at Cornell for his grandfather, in the family burial plot.