Forney was elected as clerk of the U. S. House of Representatives in 1851, serving in that position until 1855. In 1852, he became editorial writer for a Democratic organ, the Washington Daily Union. In 1854, he became a partner and helped the newspaper secure printing contracts with the House of Representatives, thereby providing it with a handsome, steady income. He left the clerkship of the House to work on Buchanan’s presidential election campaign. After his election in 1856, Buchanan was unable to secure a political position for Forney, so the journalist returned to Philadelphia in 1857 to start an independent Democratic newspaper called the Press. He soon began to support Stephen Douglas in his fight against the Buchanan administration over the Kansas question. Forney was reelected clerk of the House in 1859, and, as a Republican, served as secretary of the Senate from 1861 to 1868.

In 1861, Forney established the Washington Sunday Morning Chronicle, adding a daily edition (the Daily Morning Chronicle) in 1862. The newspaper’ s expansion was allegedly at the urging of President Lincoln, who wanted the journal to counter criticism of the administration by the New York Tribune. In the Press and the Chronicle, Forney supported Lincoln and, in the beginning of his term, Andrew Johnson. The editor soon joined the Radical Republicans, though, to become one of the Johnson’s most strident critics. Uncharacteristically, the President refused the temptation to counterattack, explaining "I do not waste my ammunition on dead ducks." But Johnson’s disparaging dismissal of Forney itself became ammunition in the arsenal of Thomas Nast and other political cartoonists who used "dead duck" to symbolize Johnson’s lack of political clout.