Siedlecki was born in 1951 in Johnstown, New York. His father, John Siedlecki, was the son of Polish immigrants and served as the head football coach at Johnstown High School for 20 years and later served as the school's principal. He next attended Union College in Schenectady, New York, where he received a Bachelor of Arts degree in history in 1974. He played at the running back and linebacker positions for the Union College football team and also played as a pitcher for the school's baseball team.