Manassah Cartright was born around 1833 in Pennsylvania to Joseph and Margaret Cartright. His father was a farmer and a veteran of the War of 1812 who owned $1,500 of real estate and $713 of personal property by 1860. Cartright grew up and attended school in Harrison, Pennsylvania. He married a woman named Fanny, and they may have had a daughter named Fanny. Cartright served in the Pennsylvania militia, and the state drafted them into military service during the Civil War. He mustered in as a private in Company B of the 171st Pennsylvania Infantry on November 2, 1862. The army stationed the men in Newbern, North Carolina, and Cartright died there of disease on March 18, 1863.