In St. Louis, Pulitzer befriended Joseph Keppler, cartoonist and founder of Puck, and Carl Schurz, a leader of the German-American community and a key Republican spokesman (whom he had known only from a distance during the Civil War).  In 1868, Schurz hired Pulitzer as the state government correspondent for his German-language daily, Westliche Post.  In December 1869, Pulitzer was elected as a Republican to fill a vacancy in the state legislature (even though he was underage), but continued his journalistic duties as well.  The next year he was fined by a court for shooting and wounding a lobbyist who had accused him of inaccurate reporting.  In 1871, he became part owner of the Westliche Post. 

In 1872, Pulitzer was appointed as one of three St. Louis police commissioners, and became involved in national politics by joining the Liberal Republican movement and supporting New York Tribune editor Horace Greeley for president.  Following Greeley’s defeat, Pulitzer thereafter identified himself with the Democratic Party, although he occasionally supported Republican candidates.  Shortly after the 1872 campaign ended, he sold his interest in the Westliche Post and used some of the profit to tour Europe for a year.  In 1875, Pulitzer campaigned across Missouri criticizing the Grant administration, and then played an active role as a delegate to the Missouri constitutional convention, particularly in lobbying for state support of public education and authority for St. Louis to craft a new city charter.  In 1876, he proved to be an effective speaker for the Democratic presidential nominee, Samuel Tilden, who carried Missouri in the election.

Pulitzer first tried to enter the New York newspaper market in 1875, unsuccessfully offering to purchase the Belletristische Journal, a German-language weekly.  The next year, he talked with Manton Marble  about possibly buying the New York World and suggested that Charles Dana publish a German version of the New York Sun.  Neither idea came to fruition, but Pulitzer was hired as a Washington correspondent for the Sun. 

When the 1876 Electoral College controversy was resolved, he again left for Europe and returned in the fall of 1877 to pass the bar, for which he had been studying intermittently over the years.  He left Washington for St. Louis, apparently planning a legal career, but bought the failed St. Louis Evening Dispatch at a sheriff’s sale, and then accepted an offer from the owner of the Evening Post to merge the newspapers into the St. Louis Post-Dispatch.  Pulitzer became sole proprietor in 1879, and made the daily into a reliable moneymaker by 1881.

Pulitzer promised to transform the Post-Dispatch into an independent champion of the people to “advocate principles and ideas rather than prejudices and partisanship.”  In reality, the newspaper manifested the owner’s populist philosophy, and leaned heavily toward Democratic policies.  His first press crusade was against wealthy property owners who he judged were not paying their fair share of taxes, so he printed parallel columns of tax returns from the rich and middle class.  The controversy brought much free publicity and many new readers to the paper. 

Pulitzer continued his political activities, unsuccessfully seeking the Democratic nomination for Congress in 1880, and serving as a delegate to the Democratic National Convention the same year.  During the 1882 elections, barbed criticism from a key Post-Dispatch reporter against a congressional nominee prompted a personal confrontation in which the journalist killed the candidate.  The incident caused the Post-Dispatch to lose readership, and Pulitzer, who fully supported his reporter, to feel increasingly unwelcome in St. Louis.

After seeking rest in Europe, Pulitzer returned to New York City in 1883, and seized an opportunity to buy the New York World.  Once the key voice for Democrats in New York City, the paper had declined in circulation and influence after Marble’s retirement in 1876, and was eventually bought by Jay Gould.  After purchasing the publication from Gould, Pulitzer professed the same idealistic principles that he had after buying the Post-Dispatch.  Under Pulitzer, the World would appeal to a mass audience by covering a wide array of news, and would crusade for what it considered the public interest against the special interests.  This dual approach often resulted in a combination of sensational news stories and serious social commentary.  

Pulitzer paid his journalists well, and sold his newspapers cheap; within two years, the World was turning a profit.  The circulation continued to rise with the newspaper's endorsement of New York governor Grover Cleveland for president in 1884, its fund-raising campaign for the Statute of Liberty’s base in 1885, and its coverage of reporter Nelly Bly’s record-breaking around-the-world trip in 1889-1890.  Over the years, the World crusaded against police brutality and political corruption, condemned the greed of large business corporations (“trusts”), and exposed the horrible conditions of tenement-house sweatshops and insane asylums (both reported by Nellie Bly).

In 1884, Pulitzer was elected to Congress as a Democrat, but he resigned, after serving just over a year, in order to focus on his newspaper duties.  The hard work and stress of his job began to take their toll on Pulitzer’s health, and a ruptured blood vessel in 1887 soon caused him to become virtually blind.  He also suffered from insomnia, diabetes, asthma, and rheumatism, and developed an acute sensitivity to noise.  After vacations to spas in Europe and America failed to relieve his distress, Pulitzer placed the World under the direction of an executive board in 1890, although he continued to have daily contact with it and the Post-Dispatch.  

In 1895, William Randolph Hearst’s New York Journal copied Pulitzer’s method of combining sensation with serious commentary, lured away some of Pulitzer’s staff, and seriously challenged the World for readership. In an effort to boost circulation, the two rival newspapers printed “extra” editions, ran often outrageous and untrue stories (dubbed “yellow journalism”), and spurred the United States toward involvement in the Spanish American War of 1898.  When Hearst ran for governor of New York in 1906, Pulitzer endorsed Republican Charles Evans Hughes (who won).

After the Spanish-American War, Pulitzer curtailed the sensationalism of the World, and in 1904 chose Frank Cobb as its new editor.  Under Cobb’s direction (1904-1923), the World gained a reputation as the nation’s leading publication for public-service journalism.  In his last years, Pulitzer arranged a $2 million gift for the establishment of a journalism school at Columbia University, and endowed the Pulitzer Prizes for outstanding work in journalism, prose, poetry, and the performing arts.  

Joseph Pulitzer died on October 29, 1911, aboard his yacht off the coast of Charleston, South Carolina.  Although he stipulated in his will that his family could never sell the World, inept oversight by his oldest and youngest sons led them to get court approval to sell the publication to the Scripps-Howard chain in 1931.  However, under his middle son, Joseph Pulitzer II, the St. Louis Post-Dispatch became one of the most respected dailies in the United States.