John Kenneth Blackwell (born February 28, 1948) is an American politician, author, and conservative activist who served as the mayor of Cincinnati, Ohio (1979–1980), the Ohio state treasurer (1994–1999), and Ohio secretary of state (1999–2007). He was the Republican candidate for governor of Ohio in 2006, the first African American major-party candidate for governor of Ohio. He is a senior fellow at the Family Research Council. He is vice president of the executive committee of the Council For National Policy and is a member of the Council on Foreign Relations.

Blackwell was born in Alliance, Ohio, the son of Dana, a part-time nurse, and George Blackwell, a meat packer. He has two brothers, Carl and Charles. He married his wife, Rosa, in 1969 while he was in college. They have three children. Blackwell is the nephew of Olympic long-jumper DeHart Hubbard, who was the first Black athlete to win a gold medal in an individual Olympic event, jumping more than 24 feet at the 1924 Paris Olympics.

Blackwell grew up in the Avondale and West End neighborhoods in Cincinnati. He attended Samuel Ach Junior High School and graduated from Hughes High School, where he met his future wife.

Blackwell attended Xavier University in Cincinnati on a football scholarship. He received a Bachelor of Science degree in psychology from Xavier in 1970 and his Master of Education degree, also from Xavier, in 1971. After college, he was invited to the Dallas Cowboys' training camp; he gave up football when told he would have to convert from linebacker to offensive lineman. He taught at Xavier from 1974 to 1991.

He has served as a trustee of Wilberforce University and Wilmington College. On April 25, 1987, Blackwell was made a Mason-on-Sight by Grand Master Odes J. Kyle Jr. of the Most Worshipful Prince Hall Grand Lodge of Ohio; thereby making him a Prince Hall Freemason. This African-American branch of Freemasonry was founded in the 19th century.

Blackwell became involved in politics through the Charter Committee, Cincinnati's third party. He was subsequently elected to and served on the Cincinnati city council. In 1978, he was elected as the mayor of Cincinnati, serving into 1980. One of his first priorities was to establish a crowd control task force, to study better methods of crowd control and injury prevention. This was in response to the deaths of 11 concert fans at a concert by the British rock group The Who at Riverfront Coliseum on December 3, 1979.

When Blackwell began to consider statewide and national offices, he became a Republican. He was appointed to serve in the administration of President George H. W. Bush as undersecretary in the Department of Housing and Urban Development, a position he held from 1989 to 1990. He returned to Cincinnati to run for the first district seat in the United States House of Representatives which was being vacated by Tom Luken. Blackwell lost to Luken's son, Charlie Luken, by a narrow 51% to 49% margin. Following his close defeat, Blackwell was appointed by President Bush as U.S. ambassador to the United Nations Commission on Human Rights. Blackwell served in that post from 1992 to 1993.

In 1994, Governor George Voinovich appointed Blackwell as Ohio state treasurer to complete the term of Mary Ellen Withrow. She had been appointed as Treasurer of the United States by President Bill Clinton. Blackwell was elected treasurer in 1994.