Having declared themselves free from British rule, John Adams and the other members of the Second Continental Congress set about forming a new government for their new country. Meanwhile, the war for freedom dragged on: George Washington recaptured New Jersey and the British saw a major defeat at Saratoga. Adams drafted what came to be known as the Plan of 1776, a framework for peace treaties and alliances that would serve as a model for coming decades. He and two others journeyed to meet with the commanding British admiral on Staten Island to attempt to negotiate a peace but found the admiral unable to grant them anything. Adams' homesickness worsened and he wished to return to his family in Braintree. He departed for home on November 11.

He would not stay home for long, however. While Adams was away on business, his wife, Abigail, opened his mail one day to discover that the Congress had elected Adams to serve as commissioner to France. He agreed to go and, through the early winter, debated whether his family should accompany him; deciding finally that the long ocean journey and the danger of being captured by the British was too great, Adams allowed only his son, John Quincy, to accompany him to Europe. They departed on February 13, 1778. The crossing took six weeks and their frigate, Boston, arrived on April 1, 1778. In France, Adams hoped to gain recognition for his country from the European governments. Humorously, though, everywhere Adams traveled in France he was introduced as "le fameux Adams" and the author of Common Sense. It was only with great difficulty that he convinced people he was not his famous cousin and he did not even bother trying to convince them that Thomas Paine, not Sam Adams, had written Common Sense.

His time in France was a difficult one, and he often whined in his diary about his partner, Benjamin Franklin, who, Adams charged, often traded the work of the commission to spend time with women. Franklin and the third commissioner had already signed a treaty with France by the time Adams arrived, so he was left with little to do. He pleaded with his cousin to be allowed to return to America, and on February 12, 1779 Adams received word that he should return home. His trip, however, had been in vain. The groundwork Adams and the other commissioners laid helped America gain allies in Europe and helped convince France to intervene in the ongoing Revolution. France, stripped of its former prestige after the humiliating French and Indian War, desperately wanted to get back at England–it found its chance in the Revolution.

Adams returned to Braintree just in time to be chosen to help draft a new Constitution for Massachusetts and the document eventually ratified by the Massachusetts Constitutional Convention in 1780 drew largely from Adams' work.

Adams barely finished his work in Massachusetts before the Continental Congress again sent him to Europe–this time in anticipation of peace negotiations with Britain. He waited anxiously in Paris again, doing little and managing to draw fire from the French for meddling in their affairs and from Franklin in response to Adams' continued comments about Franklin's ill behavior. As Adams waited for peace, the Revolutionary War drew to a close. The commander of the southern continental troops, General Nathanael Greene, eventually forced the British army, under General Cornwallis, to retreat to Yorktown. With help from the French Army and Navy, from October 6 to October 19, 1781, sixteen thousand allied troops lay siege to the city until the 6,000 British troops, who were held up in Yorktown, surrendered. It would be the last major battle of the war.

Back in Europe, the time for peace had nearly arrived. However, first, frustrated with his role in Paris, Adams traveled to the Netherlands to work on a treaty with that country. John Quincy left his father to serve as a secretary with an American delegation to Britain and his other companion for the trip, his son Charles, left Adams to return to Braintree.

After many months of hard work, Adams won recognition from the Netherlands for American independence and led the successful negotiation of a monetary loan and trade treaty with the government. He returned to Paris in October 1782 to join John Jay and Franklin in the peace discussions. Adams played a crucial role in the negotiations, continually pushing for expansion of American fishing rights in the Atlantic and for an expansion of the boundary westward. Both parties signed the Treaty of Paris on September 3, 1783. Adams remained in Europe while his secretary returned the treaty to America, and, in ill health, Adams journeyed to Bath, England. While in England, he toured the King's castle at Windsor and stood in awe of its library. Again, his nation called, and Adams rushed from England to Amsterdam and secured a second massive loan to help jump- start the new country and save its credit.

In 1785, with America now entirely free and under the governance of the Articles of Confederation, Adams became the first U.S. minister to Britain. Needless to say, his three year tour of duty in London were among the most frustrating of his life because England had little interest in improving the relationship with its newly freed colonies or in bettering trade relations. Adams made the best of his time, socializing with the minister to France, Thomas Jefferson, and writing one of his most important works, the three-volume "A Defence of the Constitutions of Government of the United States," which was finally published in 1787. Like much of his other work, the "Defence" was unpolished but contained much vital information on natural law and constitutional theory–theories that would be cited in the Constitutional Convention during the very year of the "Defence"'s publication. Despite the general American ill will towards the British, Adams praised the Parliamentary system as the "most stupendous fabric of human invention."