Strickland said in a statement Tuesday that he stands by his record as governor and wont' seek the office again.
Kasich, a former investment banker and congressman, unseated Strickland as he sought a second term in 2010. It was among the most expensive governor's race in Ohio history, with combined spending approaching $34 million.
Strickland's decision leaves Cuyahoga County Executive Ed FitzGerald and U.S. Rep. Tim Ryan among the top potential Democratic challengers to Kasich next year.
FitzGerald is a former FBI agent and mayor tapped to lead Ohio's most populous county out of scandal. Ryan is a six-term congressman from Youngstown first elected in 2002.