Before becoming Vice President, Hamlin had served as a Congressman from Maine (1843-1847) and a Senator from Maine (1848-1861), during which, he briefly resigned to become governor of Maine, holding that office from January 8, 1857 through February 25, 1857, before resigning that position to return to the Senate. After the Civil War, Hamlin was again elected as Senator, serving from 1869-1881.
"Stand fast! That has ever been my watchword, and at no time in all the history of our great and glorious republic has our heeding it been more urgent. Abraham Lincoln’s body may lie in the grave, but we shall go marching on — to victory!
"The responsibility for this great war, in which our leader gave his last full measure of devotion, lies solely at the feet of the Southern slaveocrats who conspired to take their states out of our grand Union for their own evil ends. I promise you, my friends — Abraham Lincoln shall be avenged, and those who caused his death punished in full.
Henceforward, I say this: let us use every means recognized by the Laws of War which God has put in our hands to crush out the wickedest rebellion the world has ever witnessed. This conflict is become a radical revolution—yes, gentlemen, I openly employ the word, and, what is more, I revel in it—involving the desolation of the South as well as the emancipation of the bondsmen it vilely keeps in chains.
"They have sowed the wind; let them reap the whirlwind. We are in earnest now, and have awakened to the stern duty upon us. Let that duty be disregarded or haltingly or halfway performed, and God only in His wisdom can know what will be the end. This lawless monster of a Political Slave Power shall forevermore be shorn of its power to ruin a government it no longer has the strength to rule.
"The rebels proudly proclaim they have left the Union. Very well: we shall take them at their word and, once having gained the victory Providence will surely grant us, we shall treat their lands as they deserve: not as the states they no longer desire to be, but as conquered provinces, won by our sword. I say we shall hang Jefferson Davis, and hang Robert E. Lee, and hang Joe Johnston, yes, hang them higher than Haman, and the other rebel generals and colonels and governors and members of their false Congress. The living God is merciful, true, but He is also just and vengeful, and we, the people of the United States, we shall be His instrument in advancing the right."
Hamlin and his successors instituted a policy to oppress the former Confederate States which resulted in the destruction of their economy, and racial division, that caused problems for US security as late as the 1940s.
In 1882, Hamlin was one of several prominent Republican leaders to attend a convention called by Lincoln in Chicago. He resisted Lincoln's proposal to replace hostility toward the Confederate States with workers' rights as the central plank of the party's platform. The rejection of this proposal led to Lincoln's defection to the Socialist Party and the end of the Republican Party as an effective force in American politics.