Born in Lycoming County, Pennsylvania, McKinney graduated from the College of New Jersey (now Princeton University) with an Artium Baccalaureus degree in 1848.
He served as a clerk in the Solicitor's Office of the United States Department of the Treasury in Washington, D.C., beginning in 1861.
[1] McKinney received a recess appointment from President Ulysses S. Grant on November 8, 1870, to a seat on the United States District Court for the Southern District of Florida vacated by Judge Thomas Jefferson Boynton.
He was nominated to the same position by President Grant on December 7, 1870.
He was confirmed by the United States Senate on February 18, 1871, and received his commission the same day.