DeMortie was born into slavery on May 8, 1829, in Norfolk. The names of his parents are not recorded. Described as having mixed-race ancestry and at least twice as being a Frenchman, DeMortie was a member of the DeMortier family, descendants of Haitian natives who lived in Norfolk and some of whom were freeborn. He spelled his surname DeMortie and pronounced it Demorty. When he was about ten years old, Mary Ogilvie, a Norfolk resident, purchased him from the estate of Robert B. Starke. On March 25, 1850, a few weeks before his twenty-first birthday, she emancipated him.
DeMortie had learned to read and write. According to his own later account he corresponded with antislavery activists in the North and assisted Norfolk members of the Underground Railroad in concealing nearly two dozen escaping slaves aboard merchant ships en route to Philadelphia, Pennsylvania, or New Bedford, Massachusetts. Had he been caught and convicted, he could have been reenslaved. DeMortie made one or more trips to free states to arrange financing for escapees. About 1853 he moved to Boston, Massachusetts, where for a time he was part-owner of a shoe shop. He was in the Boston crowd that failed to prevent the escaped Virginian Anthony Burns from being returned to slavery in 1854.
DeMortie supported the American Party, or Know Nothings, and then moved with other antislavery members of that party into the new Republican Party. He was often conspicuous in antislavery meetings in New England during the latter part of the decade. In 1858 DeMortie served as a vice president of a Boston meeting of black abolitionists who sent a petition to Congress protesting the Supreme Court’s Dred Scott decision. The following year he signed the call for a regional convention of African Americans to press for the right to vote in free states where black men did not have the suffrage, and he took part in a campaign to delete racial descriptions from Boston’s voting lists. DeMortie’s political connections allowed him to obtain a job in the customhouse in Boston and probably also explain his appointment as sutler of the all-black 54th Regiment Massachusetts Infantry in 1863 shortly before it embarked for action on the South Carolina coast. (A sutler travels with an army, selling provisions to soldiers.)
In Newport, Rhode Island, on January 6, 1864, DeMortie married Harriet McCabe. They had at least one son. After the American Civil War (1861–1865), DeMortie became part-owner of a Boston tailor shop. In 1865 he signed a call for sending a delegation of black men to Washington, D.C., to lobby Congress for equal rights. He also organized black workingmen to take the places of striking white railroad workers at the same wages the white men had earned. DeMortie served as a delegate to the 1868 Republican National Convention in Chicago. He entered the real estate business there but after about two years decided to move back to Virginia. By 1870 he was operating a Richmond factory that extracted oil from sassafras roots for sale to manufacturers of medicines and soap. Before leaving Illinois, DeMortie had divorced his wife, and on May 18, 1870, in Washington, D.C., he married Cordelia Downing, daughter of a wealthy African American caterer and former Newport antislavery activist. They had two daughters. His wife often spent part of the summers in Newport, as did he in some years.
Virginia Political Career
About 1872 DeMortie moved his oil factory to Burkeville, in Nottoway County. He began attending state meetings of African Americans and resumed his activity in the Republican Party. In 1874 DeMortie unsuccessfully sought the party’s nomination for the Fourth District seat in the House of Representatives. Two years later he won election to the party’s state central committee, and he again ran for the nomination for Congress from the Fourth District, consisting of Petersburg and eleven counties lying between the James River and the North Carolina border. DeMortie’s intelligence and speaking ability favorably impressed even some Democratic newspaper editors. The campaign lasted for several months and bitterly divided the district’s black and white Republicans, who on the same day in mid-August held separate conventions in Farmville and respectively nominated DeMortie and Joseph Jorgensen, the white postmaster of Petersburg. Late in September the district and state party committees endorsed Jorgensen, but DeMortie, arguing that the district’s African Americans should elect one of their own to Congress, continued to campaign. Jorgensen persuaded the president to send a company of soldiers to Petersburg to keep the threatened peace on election day, when he narrowly defeated the Conservative Party candidate. DeMortie received only a few votes in Petersburg and few or none in most of the counties except Nottoway, where he garnered less than a quarter of the votes.
DeMortie attended the 1880 Republican National Convention as an alternate delegate. The following year he was mentioned as a candidate for postmaster of Petersburg and by 1884 had been appointed a deputy collector of internal revenue. Although initially skeptical about an alliance between Republicans and the Readjusters, DeMortie joined most of the state’s other African American political leaders early in the 1880s in supporting the new party, which sought to repudiate a portion of the antebellum public debt and to redirect remaining resources in support of the public school system and other state institutions. In 1882 he unsuccessfully sought the Readjuster nomination for the House of Representatives, and in 1884 he became a member of the Readjuster state committee.
DeMortie added a sawmill to his Burkeville sassafras mill. In 1885 he paid taxes on land and personal property, including a pleasure carriage and a good-quality pocket watch, worth a total of nearly $2,250. After his mills burned a year or two later he returned to Boston, where he invested in a clothing store. At the end of the nineteenth century DeMortie participated in the congressional campaign of William Henry Moody, who introduced an unsuccessful antilynching bill in Congress in 1901 and later served as attorney general and as an associate justice of the Supreme Court of the United States. In December 1905 DeMortie spoke several times during Boston’s centennial commemoration of the birth of the abolitionist William Lloyd Garrison. DeMortie and his wife lived the final years of his life with their married daughter’s family in Newport, Rhode Island, where he died on September 3, 1914. He was buried in Woodlawn Cemetery, in Everett, north of Boston, Massachusetts.