A war hero but a reluctant politician, Grant was unanimously nominated by the Republican Party and was elected president in 1868.

The Democrats, having abandoned Andrew Johnson, nominated former New York governor Horatio Seymour for president, advocating the immediate restoration of former Confederate states to the Union and amnesty from "all past political offenses." Grant won in a landslide, collecting 214 electoral votes to Seymour's 80.

In his inaugural address, which was attended by large numbers of African Americans, Grant urged the ratification of the Fifteenth Amendment, which would prohibit the federal government and individual states from denying a citizen the right to vote based on that citizen's "race, color, or previous condition of servitude."

On March 1, 1872, President Ulysses S. Grant signed The Act of Dedication law that established Yellowstone National Park, which is widely held to be the first national park in the world.

As president, Grant stabilized the post-war national economy and created the Department of Justice in order to prosecute the Ku Klux Klan. Grant's Attorney General, Amos T. Akerman, was zealous in hunting down former Klan members. By 1872, the Klan's power had collapsed, and African Americans voted in record numbers in elections in the South.

In 1872, the Liberal Republican Party was organized to oppose Grant's re-election, nominating New York Tribune founder and editor Horace Greeley for president and Missouri governor B. Gratz Brown for vice president. The Democrats adopted the Greeley-Brown ticket and united behind the Liberal Republican platform. But Grant won easily thanks to federal prosecution of the Klan, a strong economy, debt reduction, lowered tariffs, and tax reductions. In another Electoral College landslide, he collected 286 votes to Greeley's 66.

The Civil Rights Act of 1875 was a United States federal law enacted during the Reconstruction Era in response to civil rights violations to African Americans, giving them equal treatment in public accommodations, public transportation, and to prohibit exclusion from jury service. The bill was passed by the 43rd United States Congress and signed into law by President Ulysses S. Grant on March 1, 1875. Eight years later, the Supreme Court would declare it unconstitutional.

During his presidency, Grant vetoed an unprecedented 93 bills, 4 of which were overridden by Congress. The previous record had been 29 vetoes, set by his predecessor, Andrew Johnson.

In the final year of his life, dying of throat cancer and worried constantly about leaving his wife a suitable amount of money to live on, he wrote his memoirs, which proved to be a major critical and financial success. Century magazine offered Grant a book contract with a 10 percent royalty, but Grant's friend Mark Twain, understanding how bad Grant's financial condition was, made him an offer for his memoirs which paid him an unheard-of 75 percent royalty.