[1] His father, Francis Preston Blair, Sr.,[1] was editor of The Washington Globe and a prominent figure in the Democratic Party during the Jacksonian era.

After a year of service in the Seminole War, however, he left the U.S. Army, married Caroline Rebecca Buckner of Virginia, and began studying law at Transylvania University in Lexington, Kentucky.

[1] Lincoln expected Blair, who advocated taking a firm stance with the southern states, to help balance more conciliatory members of his cabinet.

Conservative as he may have been on other aspects of the slavery issue, Blair's work in the case of Dred Scott vs. Sandford suggests a willingness to embrace more progressive viewpoints.

Under Blair's administration, such reforms and improvements as the establishment of free city delivery; the adoption of a money order system; and the use of railway mail cars were instituted, the last of which had been suggested by George B. Armstrong (d. 1871), of Chicago, general superintendent of the United States railway mail service from 1860 to his death.

Lincoln's action may have been a response to the hostility of the Radical Republican faction, which believed Blair's retirement should follow the withdrawal of John C. Frémont as a candidate in the 1864 presidential election.

In 1876, Blair, along with Matthew H. Carpenter and Jeremiah S. Black, was counsel to Secretary of War William W. Belknap during the House of Representatives investigation into the Trader post scandal.

[7] Blair asked the House Investigation Committee chaired by Hiester Clymer to drop the charges against Belknap if the latter resigned office.

Belknap was impeached by the House of Representatives for receiving illicit payments from the Fort Sill trader post on the American frontier as Secretary of War.

Belknap had been granted sole power by Congress to choose sutlers to operate lucrative trader posts that sold supplies to U.S. soldiers and Indians.