Daniel E. Sickles was born on October 20, 1819 in New York City. He studied at what is now New York University and studied law in the office of Benjamin Butler, being admitted to the New York bar in 1846. He served as a member of the New York Assembly in 1843, beginning his long and controversial political career. In 1852, he married fifteen-year-old Teresa Bagioli and, one year later, was appointed secretary of the U.S. legation in London. He served in the New York Senate from 1856 to 1857, before serving in the U.S. Congress from 1857 to 1861. His term was interrupted in 1859, when he murdered the district attorney of Washington D.C., Philip Barton Key, who was having a well-known public affair with Sickles' wife. At trial, Sickles was acquitted by implementing the first known use of the temporary insanity defense.
At the outbreak of the Civil War, Sickles was instrumental in recruiting units from New York and was appointed colonel of four regiments. In September 1861, he was promoted to brigadier general of volunteers. He commanded a brigade of the Army of the Potomac at the Battle of Seven Pines and the Seven Days Battles. He was promoted to major general on November 29, 1862 and was given command of the U.S. Army III Corps in February 1863. Sickles was the only Union corps commander who did not have a West Point education. One the second day at the Battle of Gettysburg, July 2, 1863, he violated a direct order from Gen. George Meade in the positioning of his corps. As a result, a Confederate assault smashed the III Corps, rendering them virtually useless. Sickles' right leg was shattered by a cannon ball during the fight and was amputated later that day. On July 4, he was sent back to Washington D.C., effectively ending his combat career.
Sickles' career with the army and politics was not over. He was given a role in the military reconstruction of the South. From 1865 to 1867, he commanded the Department of South Carolina, the Department of the Carolinas, the Department of the South, and the 2nd Military District. His wife died in 1867 and, in 1869, he retired from the army at the rank of major general and accepted an appointment as U.S. Minister to Spain. While in Spain, in 1871, he remarried. He and his wife, Carmina had two children and returned to the United States in 1874.
Sickles remained politically involved well into old age. In 1888-89 he was president of the New York State Board of Civil Service Commissioners, he served as sheriff of New York in 1890, and he returned to the U.S. Congress from 1893 to 1895. In 1897, he lobbied his political friends and allies and managed to have himself awarded the Congressional Medal of Honor for valor at the Battle of Gettysburg. He was active in preservation efforts at Gettysburg until his death. Sickles died in New York City on May 3, 1914 and was buried in Arlington National Cemetery.