He was a highly influential backroom politician in Texas before becoming a key supporter of the presidential bid of Wilson in 1912 by managing his campaign, beginning in July 1911.

Having a self-effacing manner, he did not hold office but was an "executive agent", Wilson's chief adviser on European politics and diplomacy during World War I (1914–1918).

House helped to make four men governor of Texas: James S. Hogg (1892), Charles A. Culberson (1894), Joseph D. Sayers (1898), and S. W. T. Lanham (1902).

A "cosmopolitan progressive" who examined political developments in Europe, House was an admirer of the British Liberal welfare reforms instigated between 1906 and 1914, noting to a friend in June 1911 that David Lloyd George is working out the problems which are nearest my heart and that is the equalization of opportunity ... .

The income tax, the employers' liability act, the old age pension measure, the budget of last year and this insurance bill puts England well to the fore.

We shall follow slowly because of the newness of conditions here and the lack of pressure.” [12] In 1912, House anonymously published a novel called Philip Dru: Administrator, in which the title character leads the democratic Western U.S. in a civil war against the plutocratic East, becoming the dictator of America and turns it into “Socialism as dreamed of by Karl Marx”.

House was offered the cabinet position of his choice (except for Secretary of State, which was already pledged to William Jennings Bryan) but declined, choosing instead "to serve wherever and whenever possible".

In the 1916 presidential election, House declined any public role but was Wilson's top campaign adviser: "he planned its structure; set its tone; guided its finance; chose speakers, tactics, and strategy; and, not least, handled the campaign's greatest asset and greatest potential liability: its brilliant but temperamental candidate.

House felt that the war was an epic battle between democracy and autocracy; he argued the United States ought to help Britain and France win a limited Allied victory.

[19] Wilson had House assemble "The Inquiry", a team of academic experts to devise efficient postwar solutions to all the world's problems.

In October 1918, when Germany petitioned for peace based on the Fourteen Points, Wilson charged House with working out details of an armistice with the Allies.

Diplomat and historian Philip Zelikow argues that House's actions and advice to Wilson in the 1916-1917 period significantly extended World War I.

The belligerents in the grip of war fever considered even discussing a peace conference a show of weakness; rejected automatically any proposal their enemy favored.

Wilson's hopeful call for a reasonable, practical "peace without victory" backfired; angered the French and English fighting for Germany's utter and decisive defeat.

The efforts to offer American mediation foundered not for lack of trying, but because the intransigent warring nations were not ready for peace—this, according to House's contemporaneous correspondence.

Then Germany's decision to resume unrestrained submarine attacks against vessels of neutral nations, together with the Zimmerman telegram offering a German-Mexican alliance on the understanding Mexico would be assisted to reconquer New Mexico, Texas, and Arizona—precipitated Wilson's decision to ask Congress to declare that a state of war existed between Germany and the United States.

[21] House helped Wilson outline his Fourteen Points and worked with the president on the drafting of the Treaty of Versailles and the Covenant of the League of Nations.

On May 30, 1919, House participated in a meeting in Paris which laid the groundwork for establishment of the Council on Foreign Relations (CFR), a private organization based in New York.

Later, he dismissed House's son-in-law, Gordon Auchincloss, from the American peace commission when it became known the young man was making derogatory comments about him.

After his death, politicians, diplomats and statesman from around the United States, Canada and the United Kingdom expressed their admiration for House and regrets about his death, including President Franklin Delano Roosevelt, Cordell Hull, Fiorello LaGuardia, Al Smith, Mackenzie King, David Lloyd George, Lord Tyrrell, and Lord Robert Cecil.