John Kenneth Blackwell (born February 28, 1948) is a former secretary of state (Ohio Secretary of State) of the U.S. state of Ohio who made an unsuccessful bid as the Republican (Republican Party (United States)) nominee for Governor of Ohio in the 2006 election. He was the first African-American to be the candidate for governor of a major party in Ohio. He is currently Vice Chairman of the Republican National Committees Platform Committee and was a candidate for chairman of the RNC.

Blackwell gained national prominence for his dual roles as Chief Elections Official of Ohio and honorary co-chair of the "Committee to re-elect George W. Bush" during the 2004 election. Allegations of conflict of interest and voter disenfranchisement led to the filing of at least sixteen related lawsuits naming Blackwell. Regarding voter disenfranchisement, a federal appellate court ruled, in agreement with Blackwell, that provisional ballots cast in the wrong polling location should not be counted in the election, but the court overturned his directive to poll workers that they refuse to issue provisional ballots unless satisfied as to the voters residence. Blackwell was also named in a 2006 lawsuit related to his offices public disclosure of the Social Security numbers of Ohio residents.

A staunch conservative, Blackwell successfully led the campaign for the 2004 Ohio Constitution Amendment (Ohio State Issue 1 (2004)) banning state recognition of same sex marriage and civil unions, despite opposition from many other Republican leaders. He is a proponent of gun ownership rights, and has stated that he is against abortion except in order to protect the life of the mother. He was defeated by Ted Strickland in the 2006 Ohio gubernatorial election (Ohio gubernatorial election, 2006).