John McLean was born in Morris County, New Jersey, on March 11, 1785, the son of Fergus McLean and Sophia Blackford. After living in a succession of frontier towns in Virginia and Kentucky, in 1797 his family settled in Warren County, Ohio.
He read law and was admitted to the bar in 1807. That same year he founded The Western Star, a weekly newspaper at Lebanon, the Warren County seat, where he practiced law. He was elected to the U.S. House, serving from March 4, 1813, until he resigned in 1816 to take a seat on the Ohio Supreme Court, to which he had been elected on February 17, 1816.
Because of his anti-slavery-extension positions, he was considered by the new Republican party as a candidate in 1856. Despite his efforts, the nomination went to John Fremont. In 1860, he tried again, winning twelve votes on the first ballot at the Republican convention in Chicago; Abraham Lincoln ultimately was nominated.
He died in Cincinnati, Ohio on April 4, 1861, at the age of 76.
His son, Nathaniel McLean, was a Union general in the Civil War.