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Early years (1841–1848)

By the end of the 1840 campaign, the Log Cabin' s circulation had risen to 80,000 and Greeley decided to establish a daily newspaper, the New-York Tribune. At the time, New York had many newspapers, dominated by James Gordon Bennett 's New York Herald, which, with a circulation of about 55,000, had more readers than its combined competition. As technology advanced, it became cheaper and easier to publish a newspaper, and the daily press came to dominate the weekly, which had once been the more common format for news periodicals. Greeley borrowed money from friends to get started, and published the first issue of the Tribune on April 10, 1841—the day of a memorial parade in New York for President Harrison, who had died after a month in office and been replaced by Vice President Tyler.

In the first issue, Greeley promised that his newspaper would be a "new morning Journal of Politics, Literature, and General Intelligence". New Yorkers were not initially receptive; the first week's receipts were $92 and expenses $525. The paper was sold for a cent a copy by newsboys who purchased bundles of papers at a discount. The price of advertising was initially four cents a line but was quickly raised to six cents. Through the 1840s, the Tribune was four pages, that is, a single sheet folded. It initially had 600 subscribers and 5,000 copies were sold of the first issue.

In the early days, Greeley's chief assistant was Henry J. Raymond, who a decade later founded The New York Times. To place the Tribune on a sound financial footing, Greeley sold a half-interest in it to attorney Thomas McElrath (1807–1888), who became publisher of the Tribune (Greeley was editor) and ran the business side. Politically, the Tribune backed Kentucky Senator Henry Clay, who had unsuccessfully sought the presidential nomination that fell to Harrison, and supported Clay's American System for development of the country. Greeley was one of the first newspaper editors to have a full-time correspondent in Washington, an innovation quickly followed by his rivals. Part of Greeley's strategy was to make the Tribune a newspaper of national scope, not merely local. One factor in establishing the paper nationally was the Weekly Tribune, created in September 1841 when the Log Cabin and The New-Yorker were merged. With an initial subscription price of $2 a year, this was sent to many across the United States by mail and was especially popular in the Midwest. In December 1841, Greeley was offered the editorship of the national Whig newspaper, the Madisonian. He demanded full control, and declined when not given it.

Greeley, in his paper, initially supported the Whig program. As divisions between Clay and President Tyler became apparent, he supported the Kentucky senator and looked to a Clay nomination for president in 1844. However, when Clay was nominated by the Whigs, he was defeated by the Democrat, former Tennessee governor James K. Polk, though Greeley worked hard on Clay's behalf. Greeley had taken positions in opposition to slavery as editor of The New-Yorker in the late 1830s, opposing the annexation of the slaveholding Republic of Texas to the United States. In the 1840s, Greeley became an increasingly vocal opponent of the expansion of slavery.

Greeley hired Margaret Fuller in 1844 as first literary editor of the Tribune, for which she wrote over 200 articles. She lived with the Greeley family for several years, and when she moved to Italy, he made her a foreign correspondent. He promoted the work of Henry David Thoreau, serving as literary agent and seeing to it that Thoreau's work was published. Ralph Waldo Emerson also benefited from Greeley's promotion. Historian Allan Nevins explained:

The Tribune set a new standard in American journalism by its combination of energy in newsgathering with good taste, high moral standards, and intellectual appeal. Police reports, scandals, dubious medical advertisements, and flippant personalities were barred from its pages; the editorials were vigorous but usually temperate; the political news was the most exact in the city; book reviews and book-extracts were numerous; and as an inveterate lecturer Greeley gave generous space to lectures. The paper appealed to substantial and thoughtful people.

Greeley, who had met his wife at a Graham boarding house, became enthusiastic about other social movements that did not last and promoted them in his paper. He subscribed to the views of Charles Fourier, a French social thinker, then recently deceased, who proposed the establishment of settlements called "phalanxes" with a given number of people from various walks of life, who would function as a corporation and among whose members profits would be shared. Greeley, in addition to promoting Fourierism in the Tribune, was associated with two such settlements, both of which eventually failed, though the town that eventually developed on the site of the one in Pennsylvania was after his death renamed Greeley.