In 1933, Knowles joined the law firm now known as Doar, Drill & Skow S.C. in New Richmond, Wisconsin. From 1935 to 1964, the firm was known as Doar & Knowles. From 1935 to 1940, he served on the
St. Croix County Board of Supervisors. Knowles was first elected to the Wisconsin State Senate in 1940, becoming Majority Leader after only two years in office in 1943, but during
World War II he took a break to serve as a lieutenant in the
U.S. Navy aboard the
USS Nevada. Following his military service, Knowles resumed serving in the
Wisconsin State Senate and returned to the leadership position for 5 additional legislative terms until his election as lieutenant governor in 1954. Knowles resigned his Senate seat and was succeeded by his brother,
Robert, who won an April 1955 special election to finish the unexpired senate term. Knowles was also a delegate to the
Republican National Convention several times. Knowles would be re-elected to a second term as lieutenant governor in 1956, but was narrowly defeated in 1958 by Democrat
Philleo Nash. But Knowles would return and defeat Nash in the 1960 election to reclaim the office for one more term. Elected governor narrowly over the
Democratic incumbent
John W. Reynolds in
1964 against the national
Lyndon B. Johnson tidal wave, he served three two-year terms from 1965 to 1971. During these years, he called out the
National Guard periodically to maintain civil order during the
University of Wisconsin's
anti-war and civil rights demonstrations. Under Knowles, the Conservation Department and Department of Resource Development were merged into the
Wisconsin Department of Natural Resources, vocational and higher education and traffic safety were prioritized, and state government was reorganized. Knowles opposed
right-to-work legislation. Knowles's brother,
Robert P. Knowles, served as
President Pro Tempore of the Wisconsin Senate during his last two terms as governor and during the first four years of Governor
Patrick Lucey's administration from 1971 to 1975. After leaving the governor's chair, Knowles became chairman of Heritage Wisconsin Corporation, a Milwaukee bank holding company. ==Personal life==