Montgomery Blair was born in Franklin County, Kentucky, in 1813. He graduated from West Point in 1835 and later saw action in the Seminole War. After leaving the army Blair studied law at Transylvania University before moving to St. Louis. A successful lawyer he was elected mayor of the city (1842-43) before moving to Washington.
An opponent of slavery Blair joined the Republican Party and in 1861 Abraham Lincoln appointed him as his Postmaster General. Blair was the only Cabinet member who urged Lincoln to reinforce Fort Sumter.
Blair was an efficient Postmaster General and was responsible for establishing military post offices, appointing stamp agents for the armies, secured passage of a bill abolishing postmasters' franking privileges, and improved the international mail system.
As the war progressed Blair became increasingly identified with the conservatives in Lincoln's government. He upset the more progressive members of the Republican Party when he made a speech calling for the separation of the races after the war. Radical Republications urged Lincoln to sack Blair but Lincoln stayed loyal to his Postmaster General.
In May, 1860 a convention of Radical Republications selected John Fremont as their candidate for president. Fremont accepted the nomination and told the audience: "Today we have in this country the abuses of a military dictation without its unity of action and vigor of execution." The idea of a radical candidate standing in the election worried Abraham Lincoln and negotiations began to persuade him to change his mind. Fremont's price was the removal of Blair from the Cabinet. On 22nd September, 1864, Fremont withdrew from the contest. The following day, Lincoln sacked Blair and replaced him with the radical, William Dennison.
Blair expected Abraham Lincoln to appoint him to the Supreme Court but was disappointed when Abraham Lincoln selected his old rival, Salmon P. Chase, instead. After the American Civil War, Blair supported the conservative policies of President Andrew Johnson and eventually joined the Democratic Party. Montgomery Blair died in 1883.