After he returned to New York City, he achieved major critical success for his monuments commemorating heroes of the American Civil War, many of which still stand.

Saint-Gaudens created works such as the Robert Gould Shaw Memorial on Boston Common, Abraham Lincoln: The Man, and grand equestrian monuments to Civil War generals: General John Logan Memorial in Chicago's Grant Park[3] and William Tecumseh Sherman at the corner of New York's Central Park.

[15] In New York, he was a member of the Tile Club, a group of prominent artists and writers, including Winslow Homer (his wife's fourth cousin), William Merritt Chase and Arthur Quartley.

In 1876, Saint-Gaudens received his first major commission: a monument to Civil War Admiral David Farragut, in New York's Madison Square; his friend Stanford White designed an architectural setting for it, and when it was unveiled in 1881, its naturalism, its lack of bombast and its siting combined to make it a tremendous success, and Saint-Gaudens' reputation was established.

Two grand equestrian monuments to Civil War generals are outstanding: to General John A. Logan, atop a tumulus in Chicago, 1894–1897, and to William Tecumseh Sherman at the corner of Central Park in New York (with the African-American model Hettie Anderson posing as an allegorical Victory), 1892–1903, the first use of Robert Treat Paine's pointing device for the accurate mechanical enlargement of sculpture models.

He was an artistic advisor to the World's Columbian Exposition of 1893, an avid supporter of the American Academy in Rome, and part of the McMillan Commission, which brought into being L'Enfant's long-ignored master plan for the nation's capital.

Through his career Augustus Saint-Gaudens made a specialty of intimate private portrait panels in sensitive, very low relief, which owed something to the Florentine Renaissance.

These included James Earle Fraser, Frances Grimes, Henry Hering, Charles Keck, Mary Lawrence, Frederick MacMonnies, Philip Martiny, Helen Mears, Robert Paine, Alexander Phimister Proctor, Louis Saint-Gaudens, Elsie Ward and Adolph Alexander Weinman.

Chosen by Theodore Roosevelt to redesign the coinage of the nation at the beginning of the 20th century, Saint-Gaudens produced an ultra high-relief $20 gold piece that was adapted into a flattened-down version by the United States Mint.

[25] Diagnosed with cancer in 1900, Saint-Gaudens decided to live at his Federal house with barn-studio set in the handsome gardens he had made, where he and his family had been spending summers since 1885, in Cornish, New Hampshire – though not in retirement.

In 1901, he was appointed a member of the Senate Park, or McMillan, Commission for the redesign of Washington, D.C.'s Mall and its larger park system, along with architects Daniel Burnham and Charles Follen McKim, and landscape architect Frederick Law Olmsted Jr.; in 1902, the Commission published their report, popularly known as the McMillan Plan.

The Cornish Art Colony Saint-Gaudens and his brother Louis attracted made for a dynamic social and creative environment.

The most famous included painters Maxfield Parrish and Kenyon Cox, architect and garden designer Charles A. Platt, and sculptor Paul Manship.

Included were painters Thomas Dewing, George de Forest Brush, dramatist Percy MacKaye, the American novelist Winston Churchill, and the sculptor Louis St. Gaudens, Augustus's brother.

Saint-Gaudens and his wife figure prominently in the 2011 book The Greater Journey: Americans in Paris by historian David McCullough.

In interviews upon the book's release, McCullough said the letters of Augusta Saint-Gaudens to her friends and family in the United States were among the richest primary sources he discovered in years of research into the lives of the American community in Paris in the late 19th century.

During World War II the Liberty ship SS Augustus Saint-Gaudens was built in Panama City, Florida, and named in his honor.

The renowned sculptor Augustus Saint-Gaudens was among those chosen for the 'Artists' category of this series and appears on this stamp, which was first issued in New York City on September 16, 1940.