Nast was born in Landau in der Pfalz, Germany, in 1840. He came to America at the age of six, and was educated first in public schools. His proficiency with drawing led him to be enrolled with Alfred Fredericks and Theodore Kaufmann at the school of the National Academy of Design. Thomas Nast's first illustrations were published in the Leslie's Weekly and the New York Illustrated News. In the spring of 1862, Nast joined the staff of the Harper's Weekly Magazine and his Civil War drawings made Nast a nationally known figure by the end of the war.

Nast worked with Harper's Weekly from 1862 to 1886, and he did his best and most famous cartoons for the magazine. During this time Nast's cartoons were associated with the policies of the Republican Party and they championed many of the progressive causes of the time. Nast was strongly in favor of Reconstruction and made many cartoons fighting for the rights of the freed African American slaves and against the harassment of the Ku Klux Klan. His cartoons extolled the Fourteenth and Fifteenth Amendment, the Civil Rights Bill of 1875, and the election of Hiram Revels, an African American, to the United States Senate in 1870.

Nast fought against the prevalent bigotry towards other minorities as well. The cartoonist felt that the provisions of the Civil Rights Bill of 1875 extended to all minorities, including Native Americans and Asian immigrants. Many of Nast's cartoons excoriate the U.S. military for preventing Native Americans from exercising the right to vote. He also criticized the laws that were erected to prevent Chinese immigrants from entering the U.S. in the later 19th Century.

Nast's most famous cartoons were those that he did against the corrupt Tweed Ring in 1871. The Tweed Ring was lead by William Marcy Tweed, the boss of New York City's Tammany Hall. As head of New York's Commission of Public Works, Tweed gave out lucrative contracts to his cronies, and he appointed his associates to key public positions to hide his corrupt practices. When Thomas Nast found out that over $200 million were being swindled out of the citizens of New York by the Tweed Ring, Nast made a series of scathing cartoons exposing the corruption of Tweed and his henchmen. Nast's cartoons were so effective that Tweed tried to bribe, then threaten Nast, but to no avail. Tweed was quoted as saying that he didn't care what the newspapers wrote about him since most of his constituents couldn't read, but they could see "them damn pictures!" Nast's cartoons created a public outcry that lead to the jailing of the Tweed Ring. Tweed himself tried to escape to Spain, but was eventually caught when police authorities recognized him from seeing a Nast cartoon.

Thomas Nast was the originator of many of the political symbols that we take for granted today. Thomas Nast St. Hill, the author of Thomas Nast: Cartoons and Illustrations wrote:

In the course of his many campaigns Thomas Nast originated or popularized several political symbols, including the Democratic donkey, the Republican elephant and the Tammany tiger. He also gave us our present-day conceptions of Uncle Sam, John Bull and Columbia. And Thomas Nast's Santa Claus, patterned after the St. Nicholas described in Clement Moore's "Night Before Christmas" poem, is the personification of the "jolly old elf" that we recognize today.

The foremost cartoonist of the period was Bavarian born Thomas Nast. He changed for the better the function and form of American caricature. His influences were European and his approach was classical, yet he developed a graphic language that translated into a uniquely American style of of political cartooning. His tremendous power as a commentator was rooted in his ability to motivate public opinion.

But the kind of modernism I mean is not a matter of inventiveness. It has to do with a questioning, irreverent attitude to life; with a persistent skepticism that sees through the official structures of society and does not pay reflexive homage to authority, whether that of church, monarch, or aristocrat; that tends, above all, to take little for granted, and to seek a continuously realistic attitude to its themes and subjects: to be, as Lenin would remark in Zurich many years later and in a very different social context, "as radical as reality itself"