[2][3] His father was a lawyer, captain of engineers during the Civil War and judge of a circuit court.

After the war, he returned to practicing law in Washington, D.C.[2][3] Mackey was elected as the commonwealth attorney of Alexandria County, Virginia, by one vote in 1904.

[3][4] While commonwealth attorney, he led raids on gambling dens and houses in Rosslyn, Jackson City and St. Asaph's in May 1904.

[7] The raids caused gambling houses in Rosslyn and Jackson City to shutter, including the poolroom at St. Asaph Racetrack.

[3] He later ran for the U.S. Congress in 1930, on a platform of states' rights and calling for the repeal of the 18th Amendment in favor of statewide control of liquor.

He was one of the organizers of the Arlington Trust Company and was a member of the Board of Trustees of George Washington University.

[3] Mackey married Mary, and had seven children, including Argyle, Joseph, Darlington, Thomas, Alice and Virginia.

[3][4] Virginia would later assume statewide control over liquor, a stance that Mackey supported later in his career.