Civil War Union Army Officer, US Congressman. Trained as a lawyer, he was admitted to the Pennsylvania Bar in 1843. He was admitted to the bar of Lehigh Co. Pa on 1/20/1843. Upon the outbreak of the Mexican War, he enlisted in the outbreak of the Mexican War, he enlisted in the Volunteer service, and served as 1st Lieutenant and Adjutant of the 1st Pennsylvania Voltigeurs regiment, with whom he was wounded at the Battle of Chapultepec (September 13, 1847). After his return, he served as Lehigh County District Attorney, and was elected as a Republican to represent Pennsylvania's 7th District in the United States House of Representatives, serving a single term from March 4, 1859 to March 3, 1861 (his seat being filled by Congressman Thomas B. Cooper). Barely a month later, in April 1861, after the outbreak of the Civil War, he helped recruit the 9th Pennsylvania Volunteer Infantry, a 3-month enlistment regiment, and was named its Colonel and commander. He led his unit in movements in Northern Virginia in June and July 1861, and was elevated to brigade command when previous commander Colonel Dixon Miles was recalled to Washington. The brigade served as part of Major General Robert Patterson's army that was detailed to block Confederate forces under General Joseph Johnston from linking up with forces under General P.G.T. Beauregard during the First Bull Run Campaign of July 1861. General Patterson failed in this task, and Colonel Longnecker's brigade, stationed in and around the Winchester, Virginia area, saw no action due to this. In late July he accompanied his force back to Pennsylvania, where he was mustered out after his enlistment expired. He returned to his law practice after the end of his field service, and died in Allentown in 1871.