Allen Shadrick was born around 1829 in North Carolina to Paschall and Lucy Shadrick. His father was a farmer. He grew up in Granville County, North Carolina, and by 1850, he was working as a farmer. He married Nancy Hayes in Granville County on February 22, 1857, and they had at least two children: John, born around 1858; and Ella, born around 1860. They settled in Cedar Creek, North Carolina, and Shadrick worked as a farmer.
He enlisted in the Confederate army on March 6, 1862, and mustered in as a private in Company E of the 46th North Carolina Infantry on April 16. The regiment took part in the Battle of Antietam and the Battle of Fredericksburg. He died of disease in Granville County on February 4, 1864.