He was born in Amherst, New Hampshire, where he worked as a printer, then left for New York City, where he started the New York Tribune. He was editor of the Tribune for the rest of his life, using it as a platform for advocacy of his causes, though he was known for his inconsistencies. He at first supported the rights of the Southern states to secede from the Union but became an abolitionist and a supporter of the North in the Civil War.
He was a Whig Congressman for three months, from 1848 to 1849. He ran unsuccessfully for election to the House of Representatives in 1850, 1868, and 1870, and for the United States Senate in 1861 and 1863. His personal guarantee of bail for Jefferson Davis did nothing to enhance his popularity: he was an unsuccessful candidate for President of the United States in 1872, advocating non-punitive treatment of the South. He was an agrarian and supported liberal policies towards settlers: one of his famous phrases was "Go West, young man".
While Greeley had been pursuing his political career, Whitelaw Reid had gained control of the Tribune. Weeks later, Greeley, in his final illness, spotting Reid, cried out "You son of a bitch, you stole my newspaper", and died. Reid reported Greeley's last words as "I know my redeemer liveth".
Greeley is buried in New York's Green-Wood Cemetery.