Siedow was born in Cheyenne, Wyoming. He began acting in his high school drama class, and later on, moved to New York City, New York, where he started appearing in theatre productions. During World War II, Siedow served with the Army Air Corps, and after the war, Siedow moved to Chicago, Illinois and started doing radio work. In September 1946, he met and married an Actress named Ruth, his wife up to his death. They had three children.
They moved to Houston, Texas soon after their marriage where Siedow continued acting, creating one of Houston's original local community theatres. He directed Houston's first production of Who's Afraid of Virginia Woolf? by Edward Albee. In 1971, Siedow appeared in his first movie, an obscure one titled The Windsplitter, playing a character named Mr Smith. He followed this with his most famous role as Drayton Sawyer in the cult film The Texas Chain Saw Massacre in 1974.
His other movie roles were as Howard Ives in the TV movie Red Alert in 1977, an unnamed role in the 1980 movie Hotwire, and as Drayton Sawyer, again, in The Texas Chainsaw Massacre 2, the sequel to The Texas Chain Saw Massacre.
Siedow died in Houston from emphysema complications in 2003, at the age of 83
