Born in Jonestown, Pennsylvania, Walter Mattern grew up in Allentown, Pennsylvania and served his country in the Army during World War I. After the war, he returned to Allentown to work for an engineering firm, but later moved to Bayonne, New Jersey, at which time he began studying art at the Pennsylvania Academy of Fine Arts summer school at Chester Springs, and at the Grand Central School of Art in New York City.

He returned to Allentown in the late 1920s, working as an engineer at various firms, and became a student at the Kline-Baum Art School, eventually becoming an instructor at the school. Beginning in the 1930s, he was an active member of the Lehigh Art Alliance and the Circulating Picture Club.

He was a close friend of Walter Baum, and often painted with him. His landscapes were painted in an impressionist style, generally with a full brush stroke, giving a thick, creamy surface to the canvas.

He exhibited at the National Academy of Design, the Pennsylvania Academy of the Fine Arts and frequently with the Kline-Baum School of artists in the Lehigh Valley. Mattern was a member of the board of directors of the Allentown Art Museum.

He never married and was financially independent.

Sources:
Alterman, James M. New Hope For American Art
http://www.bhnyfineart.com