[1][2][3][4] His grandfather Joseph Weisinger had been born in Germany but became Petersburg's mayor in 1792; his father Samuel S. Weisiger became a judge.

During the Mexican–American War, Weisinger served in the 1st Virginia Volunteers Infantry Regiment as a second lieutenant of Company E from December 3, 1846, to August 1, 1848.

By 1849, Weisinger was a leading Freemason, and helped to lay a monument honoring General George Washington in 1850 and was elected the lodge's treasurer in 1858.

David A. Weisiger began his Confederate Civil War service shortly after Lincoln's election, when he accepted a commission as a major in the 4th Infantry Battalion of the Virginia Militia, replaced as the 39th Regiment's commanding officer by Colonel John M. Davenport, who celebrated the occasion and his new officer comrades in January.

[2][3][4][9] Two of his captains were also wounded during Second Manassas, and Major John Pegram May killed, so on September 17, 1862 at the end of the Battle of Antietam, only 23 men of the 12th Virginia answered roll call.

[5] On July 30, 1864, during the Siege of Petersburg and under General Mahone's command, Weisinger's men went into counter-attack action at the Battle of the Crater with drill-order steadiness, and Wright's Georgian brigade and Sanders' Alabama brigade also cleared the Union troops stuck in the crater, causing 4,000 losses compared to 1500 Confederate casualties.

[2][3][4] In recognition of his contribution to this Confederate victory (though the siege continued), Weisiger was appointed brigadier general from the date of the battle, July 30, 1864.

[19] Late that year, as a token of their esteem for his efforts, Petersburg citizens banded together to purchase a horse for Weisinger, although such had become very expensive as a result of the siege.