During the Civil War, George supported the policies of the Lincoln administration (1861-1865).  After the war, he joined the San Francisco Times as a printer and writer.  In 1868, Overland Monthly published his essay, “What the Railroad Will Bring Us,” in which he first articulated his conviction that the American economic system fostered wealth for the few at the expense of poverty for the many.  He gained national attention on a trip to New York City when the New York Tribune published his article condemning immigrant Chinese laborers on the West Coast.  He claimed that the “heathen” and “treacherous” Chinese were unfairly taking jobs from white workers.  His remarks brought him a hero’s welcome upon returning to San Francisco.

During the 1870s, George supported the Liberal Republicans (1872), joined the American Free Trade League, wrote editorials critical of railroad subsidies and supportive of tax reform, and failed in both a bid for election to the California legislature and for an economics chair at the University of California.  He also published more detailed accounts of his economic theory in Our Land and Land Policy (1871) and Progress and Poverty (1879).  He argued that large landowners were unjustly profiting off the rent and toil of others, and urged that all taxes on business and consumers be abolished and replaced with a single steep tax on land.  The influential Progress and Poverty provoked international interest in his theory and sparked the “single-tax” movement.

A few weeks after the publication of Progress and Poverty, the Irish land war (1879-1882) began, and in 1881 George traveled to Ireland as a correspondent for the Irish World, an American newspaper.  He became popular with Irish Americans, who repeated his claims that the Irish land situation was not unique, but also applied to the United States.  Back in the United States, George wrote a series of articles for Frank Leslie’s Illustrated Newspaper in response to essays by laissez-faire economist William Graham Sumner.  In 1884-1885, Britain’s Radical Liberals sponsored George’s lecture tour in which he delivered 75 speeches in 35 cities throughout England, Scotland, and Ireland.

On October 5, 1886, George accepted the United Labor Party’s nomination for mayor of New York City (where he had moved in 1880).  Besides his land-tax, the party platform endorsed government ownership of railroads and telegraphs; higher wages, shorter hours, and better working conditions for laborers; and an end to police interference with peaceful assemblies.  The latter was a reaction to labor disputes that had culminated in Chicago's Haymarket Riot earlier in the summer.  Beside the tense labor situation, the mayoral campaign of 1886 occurred in the midst of revelations of massive corruption in the municipal government leading to the arrest of 22 aldermen.  George declared, “this government of New York City—our whole political system—is rotten to the core.” 

To face the challenge to its working-class constituency, the Tammany Hall Democratic machine selected a leader of the rival Irving Hall faction, Abram Hewitt, to run for mayor.  Hewitt attacked the Republican candidate Theodore Roosevelt as a tool of rich businessmen.  The Democratic nominee warned that “anarchists, nihilists, communists, [and] socialists” controlled the United Labor Party, and that the practical result of George’s economic theory would be “the horrors of the French Revolution and the atrocities of the Commune.”  As this cartoon's caption indicates, George himself compared the situation in contemporary American with that of France on the eve of its 1789 revolution.  

On November 2, 1886, Hewitt was elected mayor with 41% of the vote to George’s 31% and Roosevelt’s 28%.  George did best among Catholic voters and second-generation Irish and Germans, but lost the vote of the poorest and most recent immigrants to Hewitt.  Roosevelt lost a substantial number of middle-class and wealthy voters who cast ballots for Hewitt out of fear that the three-way race might result in a victory for George.

In 1887, the United Labor Party nominated George for the statewide office of secretary of state, but by that time the coalition that had supported him the previous year in his run for mayor had splintered, and he lost handily.  Nevertheless, a group of businessmen who supported George’s tax policy in the hope that it would rid them of corporate taxation organized the Single Tax League.  George himself enthusiastically backed President Grover Cleveland’s call for tariff reform, and endorsed the Democratic president’s reelection in 1888 and 1892.  While on another foreign speaking tour in December 1890, George suffered a stroke that undermined his general health.  He was able, though, to begin writing the Science of Political Economy, and to campaign for William Jennings Bryan in 1896.