McKinley was elected to the Alabama House of Representatives in August 1820.[4] the next year he moved his family from Huntsville to Florence, and so was ineligible for re-election.[5]
November 27, 1826, he was elected as a Jacksonian to finish the unexpired term of Senator Henry H. Chambers, who died in office.[7] When he sought re-election in 1830, he lost to Gabriel Moore.[4]
The number of seats on the Supreme Court was expanded from seven to nine in March 1837, as a result of the Eighth and Ninth Circuits Act.[9] This allowed President Jackson the opportunity to appoint two new associate justices, which he did on March 3, 1837, his last full day in office. The newly seated Senate of the 25th Congress confirmed both nominees; but one, William Smith, subsequently declined to serve.[10]
President Martin Van Buren offered McKinley a recess appointment to the vacant seat on April 22, 1837, and later formally nominated him to for it on September 18, 1837. McKinley was confirmed by the United States Senate on September 25, 1837, by a voice vote.[11]
McKinley was assigned to the ninth circuit, which encompassed the states of: Alabama, Mississippi, Louisiana, and Arkansas.[4]
During his 14 years on the Court, McKinley wrote 22 opinions, several of which were dissenting opinions in the interest of preserving States' rights.[4]
McKinley was married twice. In 1814, he married Juliana Bryan (d. 1822).[13] They had three children: Elizabeth, Andrew and Mary.[14] In 1824, he married Elizabeth Armistead (d. 1891). They had no children.[15]
In 1821, McKinley was appointed to serve on the original board of trustees for the University of Alabama and helped plan the campus design and curriculum.[5] He was also a founding member of the First Presbyterian Church of Florence, Alabama,[4] where he was elected as an elder in 1826.[16]
McKinley owned twelve slaves at the time of the 1850 census.[17]
McKinley moved his family to Louisville, Kentucky soon after his appointment to the Supreme Court. He later died there on July 19, 1852, at the age of 72,[4] and is buried at Cave Hill Cemetery.
^ John McKinley, United States census, 1850; Louisville Ward 7, Jefferson, Kentucky;.
^Marengo County Heritage Book Committee (2000). The heritage of Marengo County, Alabama. Clanton, Alabama: Heritage Publishing Consultants. p. 9. ISBN1-891647-58-X.