Newton was born in the city of Norfolk on August 24, 1822. His parents were Thomas Newton, who served in the House of Delegates (1796–1799) and the U.S. House of Representatives (1801–1833), and Newton’s second wife, Margaret Jordan Pool Newton. He had a half sister, Caroline Newton, by his father’s first marriage and eight full siblings, of whom three lived to adulthood. Cincinnatus W. Newton stood as an elector forin 1860. Washington Irving Newton served as a major in the U.S. cavalry, mustering out of service in October 1861 due to poor health. Another brother, Thomas Newton, is said to have traveled to California in 1848, never to be heard from again.
After attending public schools in Norfolk and receiving private instruction in mathematics, John Newton entered the the United States Military Academy at West Point, New York, in July 1838. He graduated four years later, second in a class of fifty-six. His classmates included future Union generals(ranked 17) and Abner Doubleday (ranked 24) and future Confederate general (ranked 54). After graduation, Newton stayed on at West Point for three years as an engineering instructor before serving in the Army Corps of Engineers. He specialized in military architecture, and from 1846 until 1852 helped build or improve fortifications along the Atlantic Coast and Great Lakes. With fellow Virginians and , he participated in the mostly nonshooting Mormon War in 1858. When the Civil War began, he was chief engineer of the Department of Pennsylvania.
On October 24, 1848, in New York, Newton married Anna Morgan Starr, of New London, Connecticut. The couple had eleven children, of whom at least five lived to adulthood: Virginius M. Newton, John Thomas Newton, Victor M. Newton, Thomas M. A. Newton, and Mary Newton.
Like his West Point classmates, Thomas and Cooke, and his brother, Washington Newton, Newton did not resign from the U.S. Army when Virginiain April 1861. He was commissioned a brigadier general of volunteers in September 1861 and assigned to the defenses of Washington, D.C. During the , , and ‘s subsequent in 1862, Newton commanded a brigade in the Army of the Potomac’s Sixth Corps. He was brevetted lieutenant colonel in the Regular Army for meritorious conduct at Antietam.
At Fredericksburg in December he commanded a division. The battle was such a disaster that a handful of Union generals, including Newton, conspired against Burnside. With Union general John Cochrane, Newton actually met with President Lincoln at the White House on December 30, 1862. He could not breach military protocol and tell the president directly that he wanted Burnside fired; instead, as he later told Congress, Newton emphasized “that the troops of my division and of the whole army had become entirely dispirited” and that there was a general “want of confidence in General Burnside’s military capacity.”
Burnside caught wind of what was going on and even identified the conspirators. He met with Lincoln at the White House on January 24, 1863, with his yet-unreleased General Orders No. 8, which called for the dismissal of Newton, Cochrane, and, as well as the reassignment of some others. Burnside also carried a letter of resignation, telling Lincoln he should accept one or the other. The next day, Lincoln accepted Burnside’s resignation and, to add insult to injury, in his stead placed Hooker in charge of the Army of the Potomac. Still, there were consequences for such a revolt. Cochrane resigned within a month, citing his health. Other conspirators, including Newton’s superiors William B. Franklin and William F. “Baldy” Smith, were forced out of the Army of the Potomac. Newton stayed, but his career suffered nevertheless.
Promoted to major general of volunteers in March 1863, Newton fought well in May at theduring the Chancellorsville Campaign. Two months later, he still was with the Sixth Corps when it and the Eleventh Corps were routed on the first day of the Battle of Gettysburg. Union general John F. Reynolds, the First Corps commander, was killed and Reynolds’s old West Point classmate Abner Doubleday took over. By day’s end, however, the Army of the Potomac’s commander, , had replaced Doubleday with the less-senior Newton, leaving Doubleday livid. According to the historian Stephen W. Sears, Newton was “competent” but “no John Reynolds.” Two days later, part of Newton’s First Corps formed a portion of the line that faced .
Newton continued as a corps commander until the spring of 1864 when his commission as a major general—perhaps due to his efforts against Burnside—was not confirmed. He was transferred west, where he led a division in the Fourth Corps under fellow Virginian George H. Thomas during the Atlanta Campaign. At the Battle of Peachtree Creek on July 20, 1864, he helped hold off a major attack by Confederate general John B. Hood. In October Newton was transferred again, this time to the out-of-the-way Department of Key West and the Dry Tortugas in Florida. Perhaps in an effort to revive his career, Newton devised a joint army-navy plan he hoped would lead to the surrender of the state capital at Tallahassee. He collected a thousand-man force that included the 2nd and 99th United States Colored Infantry regiments and the 2nd Florida Cavalry (U.S.) and sailed it from Key West and Cedar Key to St. Marks. From there, the men would march to Newport, Florida, and then cross the St. Marks River, destroying property as they went, as well as the railroad that linked the town to Tallahassee, eighteen miles distant.
Confederate resistance, under Brigadier General William Miller, consisted of a small force of local militia, the 2nd Florida Cavalry (C.S.), students from the West Florida Seminary (later Florida State University), and cadets from the Florida Military Institute. They managed to beat the Union troops to Newport and remove the planks from the railroad bridge there, forcing Newton to march eight miles until he found a suitable crossing—a natural bridge where the river actually ran underground for several hundred feet. But Miller beat him there, too, and on March 6, 1865, Newton ordered a full-scale attack, which failed miserably. He suffered 148 casualties compared to 3 killed, and 28 wounded for the Confederates. He blamed the navy for failing to assist him properly.
On March 13, 1865, Newton was brevetted major general in the Regular Army. On December 28 he was promoted to lieutenant colonel in the Corps of Engineers. He mustered out of volunteer service on January 15, 1866.
Newton returned to the Corps of Engineers after the war, taking charge of construction projects in New York Harbor and Lake Champlain and reporting on potential improvements in navigation of the Hudson River. He was promoted to brigadier general and became the Army’s chief of engineers in 1884. For a number of years he supervised efforts at clearing for navigation the dangerous strait on the East River in New York City between Wards Island and Astoria, Long Island. Dubbed Hell Gate by a Dutch explorer in 1614, this section of the river had been dredged and blasted for nearly fifty years leading up to one final explosion by Newton. On October 10, 1885, Newton’s daughter Mary ceremonially pressed the button that detonated almost 143 tons of explosives (34 tons of dynamine and 108.9 tons of nitrobenzene and potassium chloride). The next day, the New York Times devoted its entire front page to the blast:
A deep rumble, then a dull boom, like the smothered bursting of a hundred mighty guns far away beyond the blue horizon, rolled across the yellow river. Up, up, and still up into the frightened air soared a great, ghastly, writhing wall of white and silver and gray. Fifty gigantic geysers, linked together by shivering, twisting masses of spray soared upward, their shining pinnacles, with dome-like summits, looming like shattered floods of molten silver against the azure sky.
The explosion created a shock that was reportedly felt as far away as Princeton, New Jersey, and was one of the largest man-made blasts prior to the atomic bomb. The Times labeled it “another triumph of human skill over the resistance of nature.”
Newton retired from the Army in 1886, serving as New York City’s commissioner of public works (1886–1888) and president of the Panama Railroad Company (1888–1895). In 1886 he received the Laetare Medal from the University of Notre Dame, awarded to a practicing Catholic in honor of service to society. Newton died of chronic rheumatism and pneumonia on May 1, 1895, in New York City after a month-long illness. He is buried at West Point.