Samuel Crockett Sloan was born in Palmyra, Missouri, around 1840 to Dr. Samuel Crockett Sloan, Sr., and Pocahontas Rebecca Harrison. His father died of typhus in April 1841, and his mother followed on September 14, 1845. By 1850, Samuel and his older brother Robert were living with the McAfee family in Lewis County, Missouri. He attended school in Lewis County before enrolling at the University of Virginia in 1858. He spent the next year studying Latin, Greek, and mathematics. He left the University in 1859, and by 1860 he was living in Marion County, Missouri.

Sloan enlisted in the Union army in Helena, Arkansas, in April 1863, and served as a first lieutenant in Company I of the 33rd Missouri Infantry. At the time, the regiment was stationed near Vicksburg, Mississippi, as part of General Ulysses S. Grant’s siege of the Confederate stronghold. Sloan, however, fell ill with chronic diarrhea shortly after enlisting, and doctors declared him unfit for duty on May 31, 1863. In June, Sloan requested a leave of absence and then tendered his resignation. The army granted him a furlough but apparently never officially accepted his resignation. As a result, Sloan was listed as absent without leave from September 13 to October 10, 1863, and he was dishonorably discharged on December 2.

Sloan appealed the decision on December 26, 1863, writing that “over staying my furlough was occasioned by prolonged sickness—and as my resignation was pending and I was expecting official notification of its acceptance every day—It seemed to me that the punishment for that offence (If sickness can be called an offence) is extremely severe and uncalled for by the facts of the case.” The War Department revoked his dishonorable discharge on February 17, 1864, and restored him to command, but there is no evidence that Sloan ever rejoined his regiment.

After the war, Sloan moved to Brooklyn, New York, where he worked as a broker and became active in local Democratic politics. He married Marie Louise Clark on November 19, 1885, and she gave birth to their only child, Robert Harrison Sloan, on April 3, 1892. In 1897, Marie Louise sued him for alimony on the grounds of cruelty and mistreatment. She died on November 27, 1901, and he followed on October 14, 1903. They were both in Green-Wood Cemetery in Brooklyn, New York, though Marie was buried with her parents.