John Armor Bingham (January 21, 1815 – March 19, 1900) was an American politician who served as a Republican representative from Ohio and as the United States ambassador to Japan. In his time as a congressman, Bingham served as both assistant Judge Advocate General in the trial of the Abraham Lincoln assassination and a House manager (prosecutor) in the impeachment trial of U.S. President Andrew Johnson. He was also the principal framer of the Fourteenth Amendment to the United States Constitution.

Born in Mercer County, Pennsylvania, where his carpenter and bricklayer father Hugh had moved after service in the War of 1812, Bingham attended local public schools. After his mother's death in 1827, his father remarried. John moved west to Ohio to live with his merchant uncle Thomas after clashing with his new stepmother. He apprenticed as a printer for two years, helping to publish the Luminary, an anti-Masonic newspaper. He then returned to Pennsylvania to study at Mercer College and then studied law at Franklin College in New Athens, Harrison County, Ohio. There, Bingham befriended former slave Titus Basfield, who became the first African-American to graduate college in Ohio. They continued to correspond for many years.

Hugh and Thomas Bingham were longtime abolitionists who were both active in local politics. They initially allied with the Anti-Masonic Party, led in Pennsylvania by Governor Joseph Ritner and state representative Thaddeus Stevens. Hugh became clerk of the Mercer County court and later a perennial Whig candidate in the county known for opposing war with Mexico. Matthew Simpson, Bingham's longtime friend since childhood, became a bishop in the Methodist Episcopal Church and urged President Lincoln to issue the Emancipation Proclamation. Following Lincoln's assassination, Simpson delivered a prayer at the White House and a funeral oration at the interment ceremony in Springfield, Illinois.

After graduation, Bingham returned to Mercer, Pennsylvania, to read law with John James Pearson and William Stewart, and he was admitted to the Pennsylvania bar on March 25, 1840, and the Ohio bar by year's end. Bingham then returned to Cadiz, Ohio, to begin his legal and political career. An active Whig, Bingham campaigned for President William Henry Harrison. His uncle, Thomas, a prominent Presbyterian in the area, had served as associate judge in the Harrison County Court of Common Pleas from 1825 to 1839. The young lawyer's practice extended to Tuscarawas County, Ohio, and its seat, New Philadelphia. In 1846, Bingham won his first election as district attorney for Tuscarawas County, serving from 1846 to 1849.

Bingham's political activity continued despite the Whig Party's decline. Campaigning as candidate of the Opposition Party, he was elected to the 34th Congress, representing the 21st congressional district. In Washington, D.C., he roomed at the same boarding house as did fellow Ohio representative Joshua Giddings, a prominent abolitionist whom Bingham admired. Voters reelected Bingham to the 35th, 36th and 37th Congresses as a Republican. However, the district was one of two Ohio districts eliminated in the redistricting following the census of 1860. Bingham thus ran for reelection in what became the 16th district. Known for his abolitionist views, he lost to Democratic peace candidate Joseph W. White, and thus failed to return for the 38th Congress, in part because Union soldiers (mostly Republican-leaning) who were away from home fighting in the war were not allowed to vote by mail in Ohio. Nonetheless, the House of Representatives appointed Bingham as one of the managers of impeachment proceedings against West Hughes Humphreys.

During the Civil War, Bingham strongly supported the Union and became known as a Radical Republican. President Abraham Lincoln appointed him Judge Advocate of the Union Army with the rank of major during his hiatus from Congress, and Bingham briefly became solicitor of the United States Court of Claims in 1865. Bingham's judge advocate service was exceptional in the sense that he was a prosecutor or appellate reviewer in three significant military trials. He oversaw critical aspects of the trials of General Fitz John Porter in 1863, Surgeon General William Hammond in 1864 and the military commission trial of the Lincoln assassination conspirators in 1864.

Bingham defeated incumbent congressman Joseph Worthington White in the next congressional election. For this election, Ohio had changed its law and now allowed soldiers away from home to vote by mail. Bingham returned to serve in the 39th Congress, which first met on March 4, 1865.

The following month, the capital fell into chaos as John Wilkes Booth assassinated President Abraham Lincoln, and Booth's co-conspirator Lewis Powell severely injured Secretary of State William H. Seward on the night of April 14, 1865. Booth died on April 26, 1865, from a gunshot wound. When the trials for the conspirators were ready to start, Bingham's old friend from Cadiz, Edwin Stanton, appointed him to serve as Assistant Judge Advocate General along with General Henry Burnett, another Assistant Judge Advocate General, and Joseph Holt, the Judge Advocate General.