In June 1774, John Adams was elected a delegate to the First Continental Congress. The move came in the last moments of the Massachusetts General Court's session. To enforce the Coercive Acts, British General Thomas Gage replaced Thomas Hutchinson as governor, vetoed Adams and twelve other members of the General Court and adjourned it to Salem, a safe loyalist area. But, before he did, Adams and four others were elected to be delegates to the Congress.

The Congress was set to act on more than a decade of incursions on colonial rights and freedoms; there would be no more inaction. The American Revolution is unique among political revolutions in history, for its organized nature ensured that the same men who began the revolution would stand as the country's new leaders when the revolution was over. Partly, this can be attributed to the points earlier described: that the Revolution, far from being a rebellion of radicals, was more like a reasserting of earlier granted rights. Liberty and freedoms that were once promised would now be collected.

Still unsure of the future, however, the Congress agreed that the colonies could not back down from their fight with Parliament. None looked forward to a future free of British rule, for most delegates were proud Englishmen. However, they recognized that natural law dictated their move. Appointed after the Parliament passed the Coercive and Intolerable Acts, which, among other moves, closed the Port of Boston until the tea spilled during the Boston Tea Party had been paid for, the delegates to Congress found themselves under pressure to act.

On Monday, August 29, the delegates arrived in Philadelphia, hot, tired and dusty from a long ride from Boston. Before the Congress convened on September 5, Adams warily got to know his fellow fifty-five delegates. With the exception of Virginia, an ardent patriotic supporter, other colonies were less organized and less virulent in their dislike of Parliament–prompting caution on many fronts. A day after Congress convened, however, word reached Philadelphia that Gage had seized the militia magazines in Boston, garnering anger and sympathy for the Bostonians. The Congress's progress was "slow as snails," Adams wrote. Only Samuel Adams wanted full independence from Britain. Joseph Galloway even suggested a joint British-American legislature. Eventually, Adams helped draft the Declaration of Rights and Grievances, the most important document to proceed the Declaration of Independence. The Congress also passed non- importation agreements to take effect on December 1, 1774 before it adjourned on October 26. Adams left Philadelphia, prepared never to return–only to find himself reelected to a second term at the Congress almost as soon as he returned to Boston.

Over the course of the winter, Adams wrote his masterful Novanglus essay, an examination of the British Empire and Parliament, in response to loyalist letters in the newspapers. The essay marked a major advance in Adams' thinking. Whereas he had previously called for English liberties, he now called for natural liberties, distancing himself from England. Far more than the rights of an Englishman, Adams now advocated for the same thing–but in the guise of basic rights guaranteed to all men. Adams now foresaw an independent commonwealth.

The Second Continental Congress convened on May 10, 1775, joined now by delegates Thomas Jefferson of Virginia, John Hancock of Massachusetts, Benjamin Franklin and James Wilson of Pennsylvania. The group together was more pessimistic than before: the earlier declaration had failed to elicit a response and British troops continued to rule Boston. Adams proposed that George Washington, a delegate from Virginia–the only man to appear in Congress in his military uniform–be appointed to head-up the continental forces and Congress subsequently approved ten companies of riflemen to join the American forces in Boston. Despite officially taking up arms against the British, it would be another year before the Congress would come to declare itself independent. The delegates signed the Olive Branch Petition, a last-ditch effort to restore peace with the King.

After the war began, 1775 was a rough year for the colonists: Parliament closed the colonies to trade; Washington laid siege to Boston after the Battle of Bunker Hill; an expedition to capture Montreal failed; retreating forces in the South burned Norfolk; the war looked grim. John Adams helped start the American Navy, a cause that would remain dear to him forever. He also began studying political theory in depth and formulating his own ideas, which would help the new America formulate a government. As the colonies turned to the Continental Congress for a blueprint for the new government, Adams stood ready to offer a thorough lesson in self-governance and natural rights.

On June 7, 1776, with no hope left, Richard Henry Lee of Virginia moved for independence. Adams, Jefferson, Franklin, Roger Sherman and Robert R. Livingston were appointed to draw up the declaration. Independence was voted upon July 2 and the Declaration of Independence was ratified on July 4. With a heavy heart, the Congress had at last broken with the King.