A Republican, McKinstry served under Governor David P. Lewis of the same political party from 1872 to 1874.

[1] He was the last Republican to serve as Lieutenant Governor until Steve Windom was sworn-in 125 years later.

A native of Augusta, Georgia, McKinstry moved to Mobile, Alabama, to live with relatives at the age of fourteen.

Two years later, in 1847, McKinstry was elected colonel of the 48th Alabama Infantry Regiment, 9th Brigade, 4th Division of the State militia.

[1] In February 1873 McKinstry instigated a power grab when he manipulated parliamentary rules to deny Democrats control over the state senate.