Andrew Gregg Curtin was born in Bellefonte, Pennsylvania. After establishing a law practice, he joined the Whig party and campaigned on behalf of several of their influential candidates. His first public office was Secretary of the Commonwealth, followed by a stint as Secretary of the Public Schools. He switched his political allegiance from the Whigs to the new Republican Party in 1860 and was instrumental in securing the Republican presidential nomination for Abraham Lincoln in May of that year.
He himself agreed to run for governor of Pennsylvania on the Republican ticket and, despite a strong Democratic opponent, won the election by a large margin, serving two terms as governor, from 1861-1867. His victory was instrumental in swinging Pennsylvania's critical electoral votes to Lincoln in the presidential election a month later.
During the Civil War, Curtin became a close friend and confidante of the president, visiting the White House several times to discuss the war effort. Also during the Civil War, Curtin organized the Pennsylvania reserves into combat units, and oversaw the construction of the first Union military camp for training militia, a facility that more than 300,000 men passed through during the four years of war. In September 1862, Curtin convened the Loyal War Governors' Conference, during which 13 governors of Union states met to discuss the war effort, state troop quotas, and support for the President Lincoln and the Emancipation Proclamation.
Curtin was also very active during the Gettysburg Campaign, working with the Union military leadership to delay Robert E. Lee's advance through Pennsylvania and prevent him from crossing the Susquehanna River. After the Battle of Gettysburg, Governor Curtin was the principal force behind the establishment of the Soldiers' National Cemetery and was seated with President Lincoln when he delivered the Gettysburg Address at the cemetery's dedication on November 19, 1863.
At the end of his second term as governor, Curtin accepted the ambassadorship to Russia in 1869. He returned to America in 1872 and supported the presidential candidacy of Horace Greeley, an action which alienated him from many leading Republicans, prompting Curtin to join the Democratic Party. Defeated in an 1878 bid for Congress, he ran again in 1880 and won the first of three consecutive terms in the House of Representatives.