On Christmas Day, Adams sent Elizabeth Sherman Cameron, a longtime friend and confidant, one of Clover's favorite pieces of jewelry requesting that she "sometimes wear it, to remind you of her." Just before the end of the year, Adams moved into his newly completed mansion next door at 1603 H Street (Figure 1, B) designed by his old friend, Henry Hobson Richardson, one of the most prominent Architects of his day.

Adams's The History of the United States of America (1801 to 1817) (9 vols., 1889–1891) has been called "a neglected masterpiece" by Garry Wills, and "A history yet to be replaced" by C. Vann Woodward. It is a highly detailed history of the Jefferson and Madison administrations, with a focus on diplomacy. Wide praise was given for its literary merit, especially the opening five chapters of volume 1, describing the nation in 1800. These chapters have also been criticized; Noble Cunningham states flatly, "Adams misjudged the state of the nation in 1800." In striving for literary effect, Cunningham argues, Adams ignored the dynamism and sophistication of the new nation.

He was born in Boston, the son of Charles Francis Adams, Sr. (1807–1886) and Abigail Brooks (1808–1889) into one of the country's most prominent families. Both his paternal grandfather, John Quincy Adams, and great-grandfather, John Adams, one of the most prominent among the Founding Fathers, had been U.S. Presidents; his maternal grandfather, Peter Chardon Brooks, was a millionaire; and another great-grandfather, Nathaniel Gorham, signed the Constitution.

John Quincy Adams (1833–1894) was a graduate of Harvard (1853), practiced law, and was a Democratic member for several terms of the Massachusetts general court. In 1872, he was nominated for vice President by the Democratic faction that refused to support the nomination of Horace Greeley.

Charles Francis Adams Jr. (1835–1915) fought with the Union in the Civil War, receiving in 1865 the brevet of brigadier general in the regular army. He became an authority on railway management as the author of Railroads, Their Origin and Problems (1878), and as President of the Union Pacific Railroad from 1884 to 1890.

Brooks Adams (1848–1927) practiced law and became a Writer. His books include The Law of Civilization and Decay (1895), America's Economic Supremacy (1900), and The New Empire (1902).

After his graduation from Harvard University in 1858, he embarked on a grand tour of Europe, during which he also attended lectures in civil law at the University of Berlin. He was initiated into the Phi Kappa Psi Fraternity as honorary member at the 1893 Columbian Exposition by Harris J. Ryan, a judge for the exhibit on electrical engineering. Through that organization, he was a member of the Irving Literary Society.

Adams returned home from Europe in the midst of the heated presidential election of 1860, which also was the year his Father, Charles Francis Adams, Sr., sought re-election to the US House of Representatives. He tried his hand again at law, taking employment with Judge Horace Gray's Boston firm, but this was short-lived. After his successful re-election, Charles Francis asked Henry to be his private secretary, continuing a father-son pattern set by John and John Quincy and suggesting that Charles Francis had chosen Henry as the political scion of that generation of the family. Henry shouldered the responsibility reluctantly and with much self-doubt. "[I] had little to do", he reflected later, "and knew not how to do it rightly." During this time, Adams was the anonymous Washington correspondent for Charles Hale's Boston Daily Advertiser.

On March 19, 1861, Abraham Lincoln appointed Charles Francis Adams, Sr. United States Ambassador to the United Kingdom. Henry accompanied his Father to London as his private secretary. He also became the anonymous London correspondent for the New York Times. The two Adamses were kept very busy, monitoring Confederate diplomatic intrigues and trying to obstruct the construction of Confederate commerce raiders by British shipyards (see Alabama Claims). Henry's writings for the Times argued that Americans should be patient with the British. While in Britain, Adams was befriended by many noted men, including Charles Lyell, Francis T. Palgrave, Richard Monckton Milnes, James Milnes Gaskell, and Charles Milnes Gaskell. He worked to introduce the young Henry James to English society, with the help of his closest and lifelong friend Charles Milnes Gaskell and his wife Lady Catherine (nee Wallop).

In 1868, Henry Adams returned to the United States and settled in Washington, DC, where he began working as a Journalist. Adams saw himself as a traditionalist longing for the democratic ideal of the 17th and 18th centuries. Accordingly, he was keen on exposing political corruption in his journalism.

In 1870, Adams was appointed professor of medieval history at Harvard, a position he held until his early retirement in 1877 at 39. As an academic Historian, Adams is considered to have been the first (in 1874–1876) to conduct historical seminar work in the United States. Among his students was Henry Cabot Lodge, who worked closely with Adams as a graduate student.

On June 27, 1872, Clover Hooper and he were married in Beverly, Massachusetts, and spent their honeymoon in Europe, much of it with Charles Milnes Gaskell at Wenlock Abbey in Shropshire, England. Upon their return, he went back to his position at Harvard, and their home at 91 Marlborough Street, Boston, became a gathering place for a lively circle of intellectuals. Adams was elected a Fellow of the American Academy of Arts and Sciences in 1875. In 1877, his wife and he moved to Washington, DC, where their home on Lafayette Square, across from the White House, again became a dazzling and witty center of social life. He worked as a Journalist and continued working as a Historian.

Henry Adams first met Elizabeth Cameron in January 1881 at a reception in the drawing room of the house of John and Clara Hay. Elizabeth was considered to be one of the most beautiful and intelligent women in the Washington area. Elizabeth had grown up as Lizzie Sherman, the daughter of Judge Charles Sherman of Ohio, the niece of Secretary of the Treasury John Sherman in Hayes's cabinet and the niece of General william Tecumseh Sherman. Her family had pressured Lizzie into a loveless marriage, but brokered a prenuptial agreement with Senator J. Donald Cameron which provided her with the income from $160,000 worth of securities, a very large amount in 1878, equivalent to about $3,970,000 worth in 2017. The arranged marriage on May 9, 1878, united the reluctant 20-year-old beauty with a 44-year-old widower with six children. Eliza, his eldest, who had served as her father's hostess, was now displaced by a stepmother the same age. The children never accepted her. The marriage was further strained by the Senator's coarseness and indifference and his fondness for bourbon.

In the 1880s, Adams wrote two novels, starting with Democracy, which was published anonymously in 1880 and immediately became popular. (Only after Adams's death did his publisher reveal his authorship.) His other novel, published under the nom de plume of Frances Snow Compton, was Esther, whose heroine was believed to be modeled after his wife.

Henry Adams initiated a correspondence with Lizzie on May 19, 1883, when her husband and she departed for Europe. That letter reflected his unhappiness with her departure and his longing for her return. It was the first of hundreds to follow for the next 35 years. They would record a passionate yet unconsummated relationship. On December 7, 1884, one year before Clover's suicide, Henry Adams wrote to Lizzie, "I shall dedicate my next poem to you. I shall have you carved over the arch of my stone doorway. I shall publish your volume of extracts with your portrait on the title page. None of these methods can fully express the extent to which I am yours."

In 1884, Adams was elected a member of the American Antiquarian Society. In 1894, Adams was elected President of the American Historical Association. His address, entitled "The Tendency of History", was delivered in absentia. The essay predicted the development of a scientific approach to history, but was somewhat ambiguous as to what this achievement might mean.

Henry, his brother, Charles Francis Adams, Clover's brother Edward, and her sister Ellen, with her husband Ephraim Gurney, were the attendees at a brief funeral Service held on December 9, 1885, at the house on Lafayette Square. Interment services followed at Rock Creek Cemetery, but the actual burial was postponed until December 11, 1885, because of the inclement weather. A few weeks later, Adams ordered a modest headstone as a temporary marker.

In 1904, Adams privately published a copy of his "Mont Saint Michel and Chartres", a pastiche of history, travel, and poetry that celebrated the unity of medieval society, especially as represented in the great cathedrals of France. Originally meant as a diversion for his nieces and "nieces-in-wish", it was publicly released in 1913 at the request of Ralph Adams Cram, an important American Architect, and published with support of the American Institute of Architects.

He published The Education of Henry Adams in 1907, in a small private edition for selected friends. For Adams, the Virgin Mary was a symbol of the best of the Old World, as the dynamo was a representative of modernity. Only following Adams's death was The Education made available to the general public, in an edition issued by the Massachusetts Historical Society. It ranked first on the Modern Library's 1998 list of 100 Best Nonfiction Books and was named the best book of the 20th century by the Intercollegiate Studies Institute, a conservative organization that promotes classical education. It was awarded the Pulitzer Prize in 1919. Some center-right intellectuals view the book critically. Conservative Journalist Fred Siegel considered the worldview expressed therein to be rooted in resentment of America's middle class. "Henry Adams," wrote Siegel, "grounded the intellectual's alienation from American life in the resentment that superior men feel when they are insufficiently appreciated in America's common-man culture."

In his 1909 manuscript The Rule of Phase Applied to History, Adams attempted to use Maxwell's demon as a historical metaphor, though he seems to have misunderstood and misapplied the principle. Adams interpreted history as a process moving towards "equilibrium", but he saw militaristic nations (he felt Germany pre-eminent in this class) as tending to reverse this process, a "Maxwell's Demon of history."

In 1910, Adams printed and distributed to university libraries and history professors the small volume A Letter to American Teachers of History proposing a "theory of history" based on the second law of thermodynamics and the principle of entropy. This, essentially, states that all Energy dissipates, order becomes disorder, and the earth will eventually become uninhabitable. In short, he applied the physics of dynamical systems of Rudolf Clausius, Hermann von Helmholtz, and william Thomson to the modeling of human history.

In 1912, Adams suffered a stroke, perhaps brought on by news of the sinking of the Titanic, for which he had return tickets to Europe. After the stroke, his scholarly output diminished, but he continued to travel, write letters, and host dignitaries and friends at his Washington, DC, home. Henry Adams died at age 80 in Washington, DC. He is interred beside his wife in Rock Creek Cemetery, Washington, DC.

Adams made many attempts to respond to the criticism of his formulation from his scientific colleagues, but the work remained incomplete at Adams's death in 1918. It was published posthumously.

Adams's wife, Clover, who had written a weekly letter to her Father throughout her marriage except for the brief hiatus during her breakdown along the Nile, never mentioned concerns or suspicions about Henry's relationship with Lizzie. Nothing in the letters of her family or circle of friends indicates her distrust or unhappiness with her husband in this matter. Indeed, after her death, Henry found a letter from Clover to her sister Ellen which had not been posted. The survival of this letter was assured by its contents which read, "If I had one single point of character or goodness, I would stand on that and grow back to life. Henry is more patient and loving than words can express—God might envy him— he bears and hopes and despairs hour after hour—Henry is beyond all words tenderer and better than all of you even."