Weisiger was born 23 December 1818 in Chesterfield County Virginia. He moved to Petersburg, Virginia as a young adult and established himself in business. In November of 1846 he helped recruit a company, of which he was elected senior second lieutenant, and headed off to fight in Mexico. Before being mustered out in August of 1848 at Fort Monroe, Weisiger had risen to the regimental adjutancy. He returned to Petersburg and his business pursuits.
In May 1853 he was unanimously elected colonel of the 39th Virginia militia regiment. With war on the horizon a battalion of volunteers was formed in late 1860 with Weisiger in command. On 20 April 1861 this battalion along with a battery of artillery, both under Weisiger's command, arrived at Norfolk, Virginia. There presence helped lead to the Union force's decision to evacuate the navy yard. On 9 May 1861 Weisiger was appointed colonel in the Confederate army. His battalion, now at regimental strength, was designated the 12th Virginia. When Confederate forces evacuated Norfolk in mid-1862, the 12th VA was assigned to Drewry's Bluff and aided in the repulse of Federal gunboats attempting to move on Richmond. Weisiger and the 12th VA then joined the Army of Northern Virginia and fought at Seven Pines and during the Seven Days. Following the end of the Peninsula campaign Weisiger and the 12th VA remained near Richmond as the rest of Robert E. Lee's army moved northward.
In late August 1862 the 12th was ordered to rejoin Lee's army. Brigaded under the command of Brigadier General William Mahone, with the 6th, 16th and 41st VA regiments the 12th fought on the right at Second Manassas. When Mahone was wounded Weisiger took over command of the brigade. While moving the brigade to assist the brigade commanded by Brigadier General Ambrose R. Wright, Weisiger was severely wounded. He would not return to active duty until 1864. On 6 May 1864, the second day in the Wilderness, Weisiger would again gain brigade command following the wounding of James Longstreet when other officers moved up. Weisiger would remain in command of the brigade, part of Mahone's division, until being surrendered at Appomattox, fighting at Spotsylvania, Cold Harbor, and nearly all the battles around Petersburg. In recognition of his gallantry during the 30 July 1864 Battle of the Crater, where he again was wounded, Weisiger was promoted to brigadier general.
During the war he had been wounded three times and had two horses shot from under him. Following the war he returned to his business pursuits and spent time as a bank cashier. He died 23 February 1899 in Richmond.