Nicholas Criswell was born on July 30, 1819, in Maryland to Rachel Criswell. He married Mary Ann Poole on February 17, 1841, and they had at least six children: Martha, born around 1841; Thomas, born around 1843; Julia, born around 1844; Rufus, born around 1844; William, born around 1847; and Mary, born around 1849. They lived in Howard, Maryland, and Criswell worked as a farmer. His wife died in the early 1850s.
Criswell moved to Barnesville, Ohio, in the 1850s, and he married Frances A. Knight on June 29, 1854. Their daughter Laura was born around 1858. In the 1850s, he began working as an engineer for the Baltimore & Ohio Railroad. In 1858, his engine overturned, and he narrowly escaped death. According to one account, “the escaping steam scald[ed] him in such a fearful manner that he covered between life and death for many months.” He eventually recovered and resumed his work. He “always commanded the respect of the officials and was well liked by the boys along the line of the road.” He died in a railway accident on May 10, 1886.