Between 9 and 10 p.m. on the night of April 18, 1775, Joseph Warren told Revere and William Dawes that the king's troops were about to embark in boats from Boston bound for Cambridge and the road to Lexington and Concord. Warren's intelligence suggested that the most likely objectives of the regulars' movements later that night would be the capture of Adams and Hancock. They did not worry about the possibility of regulars marching to Concord, since the supplies at Concord were safe, but they did think their leaders in Lexington were unaware of the potential danger that night. Revere and Dawes were sent out to warn them and to alert colonial militias in nearby towns.[42][43]

In the days before April 18, Revere had instructed Robert Newman, the sexton of the North Church, to send a signal by lantern to alert colonists in Charlestown as to the movements of the troops when the information became known. In what is well known today by the phrase "one if by land, two if by sea", one lantern in the steeple would signal the army's choice of the land route while two lanterns would signal the route "by water" across the Charles River (the movements would ultimately take the water route, and therefore two lanterns were placed in the steeple).[44] Revere first gave instructions to send the signal to Charlestown. He then crossed the Charles River by rowboat, slipping past the British warship HMS Somerset at anchor. Crossings were banned at that hour, but Revere safely landed in Charlestown and rode to Lexington, avoiding a British patrol and later warning almost every house along the route. The Charlestown colonists dispatched additional riders to the north.[43][45]

Riding through present-day Somerville, Medford, and Arlington, Revere warned patriots along his route, many of whom set out on horseback to deliver warnings of their own. By the end of the night there were probably as many as 40 riders throughout Middlesex County carrying the news of the army's advance. Revere did not shout the phrase later attributed to him ("The British are coming!"): his mission depended on secrecy, the countryside was filled with British army patrols, and most of the Massachusetts colonists (who were predominantly English in ethnic origin)[46] still considered themselves British.[47][48] Revere's warning, according to eyewitness accounts of the ride and Revere's own descriptions, was "The Regulars are coming out."[49] Revere arrived in Lexington around midnight, with Dawes arriving about a half-hour later. They met with Samuel Adams and John Hancock, who were spending the night with Hancock's relatives (in what is now called the Hancock–Clarke House), and they spent a great deal of time discussing plans of action upon receiving the news. They believed that the forces leaving the city were too large for the sole task of arresting two men and that Concord was the main target.[50] The Lexington men dispatched riders to the surrounding towns, and Revere and Dawes continued along the road to Concord accompanied by Samuel Prescott, a doctor who happened to be in Lexington "returning from a lady friend's house at the awkward hour of 1 a.m."[43][51]

Revere, Dawes, and Prescott were detained by a British Army patrol in Lincoln at a roadblock on the way to Concord.[43] Prescott jumped his horse over a wall and escaped into the woods; he eventually reached Concord. Dawes also escaped, though he fell off his horse not long after and did not complete the ride.[52]

The equestrian statue of Paul Revere in North End, Boston by Cyrus Dallin was unveiled on September 22, 1940.

Revere was captured and questioned by the British soldiers at gunpoint. He told them of the army's movement from Boston, and that British army troops would be in some danger if they approached Lexington, because of the large number of hostile militia gathered there. He and other captives taken by the patrol were still escorted east toward Lexington, until about a half mile from Lexington they heard a gunshot. The British major demanded Revere explain the gunfire, and Revere replied it was a signal to "alarm the country". As the group drew closer to Lexington, the town bell began to clang rapidly, upon which one of the captives proclaimed to the British soldiers "The bell's a'ringing! The town's alarmed, and you're all dead men!"[53] The British soldiers gathered and decided not to press further towards Lexington but instead to free the prisoners and head back to warn their commanders.[54] The British confiscated Revere's horse and rode off to warn the approaching army column. Revere walked to Rev. Jonas Clarke's house, where Hancock and Adams were staying. As the battle on Lexington Green unfolded, Revere assisted Hancock and his family in their escape from Lexington, helping to carry a trunk of Hancock's papers.[55]