Eacker was admitted to the New York bar at age 21. He soon built his practice in Manhattan into a lucrative business, allowing him to take a house on Wall Street and employ a married couple as his valet and housekeeper. He gained popularity in New York City's well-to-do social circles as a lawyer, Freemason, cavalry captain, and fire brigade inspector. For an unknown offense in 1798, which historian Eric Monkkonen interprets as an earlier duel or conflict, Eacker appeared in court and paid a recognizance, likely as a bond for good behavior. In 1801, Eacker was appointed as a master in the New York Court of Chancery, then the highest court in the state.
Eacker was selected in 1801 to deliver the Fourth of July oration at an Independence Day celebration held in New York City by a brigade of the New York State Militia, the Tammany Society, and two of the city's labor organizations, the Mechanics' Society and Coopers' Society. The Tammany Society, better known as Tammany Hall, was a Democratic-Republican partypolitical organization that Aaron Burr had built into a political machine. In politics, Eacker was known to be aligned with Burr. According to a supporter, the speech that Eacker delivered was commended by "nearly everybody," except for partisans who were "blinded... to every virtue" by "party spirit, which at that time was very bitter". Some accounts questioned whether the speech was critical of Alexander Hamilton, as it was later characterized; according to a 19th century historian who relied on Eacker's younger brother as a source, the speech was entirely patriotic and did not name or allude to Hamilton. On November 20, 1801, a Friday night, Eacker attended a play at the Park Theatre with his fiancée Harriet Livingston, a daughter of Walter Livingston and Cornelia Schuyler. Philip Hamilton and Stephen Price approached or entered Eacker's box together and loudly ridiculed him. Eacker called them "damned rascals", and in response to that insult, as was not uncommon at the time, they each challenged Eacker to a duel. Price faced the 27-year-old Eacker in a duel in Weehawken, New Jersey on November 22. Four shots were exchanged, but neither party was injured. At the same location on the following day, Eacker fatally shot the 19-year-old Hamilton in a second duel. Philip refused to raise his pistol to fire after he and Eacker had counted ten paces and faced each other, following his father’s advice to engage in a delope. Eacker, following suit, did not shoot either. For the first minute, both men stood, doing nothing, both refusing to shoot. After a minute, Eacker finally raised his pistol, and Philip did the same. Eacker shot and struck young Hamilton above his right hip. The bullet went through his body and lodged in his left arm. In what may have been an involuntary spasm, Philip also fired his pistol before he hit the ground, but this bullet did nothing. In a letter to Rufus King, Robert Troup wrote of Alexander Hamilton, "Never did I see a man so completely overwhelmed with grief as Hamilton had been." Nevertheless, after Philip's death, the elder Hamilton was said to be civil and professional in his relationship with Eacker. Hamilton would die in a duel with Aaron Burr only a few years later, on July 11, 1804, on the same dueling ground in Weehawken.
Eacker died on January 4, 1804. His death was attributed to consumption, or tuberculosis. According to Eacker's brother, the prolonged illness began in January 1802 on a bitterly cold night when Eacker fought a raging fire with his brigade, and contracted a severe cold that "settled upon his lungs" until his death. His remains were interred at St. Paul's Chapel with military honors, and his funeral procession included members of the military, fire brigade, and the Howard Lodge of Freemasons. Eacker and his fiancée never married. In January 1808, Harriet Livingston married the steamboat inventor Robert Fulton, with whom she had four children.
In popular culture
Eacker appeared as a minor character in the 2015 Broadway musical Hamilton, in which the musical number "Blow Us All Away" dramatized his duel with Philip Hamilton. The role of Eacker was originated on Broadway by a member of the show's ensemble, Ephraim M. Sykes, who also appears as Eacker on the original cast recording.
