Early in his career, he worked for Cravath, Swaine & Moore and served as special assistant attorney general to the New York State Crime Commission.
Later in his professional career, he was "of counsel" to the law firm of Hollyer, Brady, Smith, Troxell, Barret, Rockett, Hines, and Mone.
During World War II, Weyher served in the European theater in the U.S. Army, becoming a first sergeant and earning two battle stars.
According to Harvard Law School classmate Leon Baker, Weyher "was the first sergeant of a secret 120-member elite intelligence unit, which operated behind enemy lines."
His interest in the Pioneer Fund originated from its opposition to the Supreme Court's decision in Brown v. Board of Education.