For gallant and meritorious conduct at Molino del Rey, he was brevetted to first lieutenant on September 8, 1847, receiving a promotion to the full rank in January 1848, when he was briefly assigned to duty in Pascagoula, Mississippi.

During the 1862 Peninsula Campaign in Virginia, Floyd-Jones commanded the 11th Infantry at the battles of Yorktown, Gaines Mill and Malvern Hill.

During the Maryland Campaign, his regiment was lightly engaged at the Battle of Antietam, where they took a position immediately east of Sharpsburg.

Floyd-Jones was active in the Rappahannock Campaign and the Mud March, then went into winter camp prior to seeing action again at the Battle of Chancellorsville.

Following sick leave, he was assigned as Acting Assistant Inspector General and Judge Advocate of the Department of Arkansas from December 1866 to February 1867.

He was married twice: First, on June 24, 1852, to Laura Jane "Jennie" Whitney (1827–1852), of Rochester, New York, who died only three months after their wedding while Floyd-Jones was stationed in Washington Territory; Second, on April 29, 1878, to Minnie Oglesby (1858–1929), of New Orleans.

He documented these journeys in letters home, and frequently had his observations and descriptions of these faraway places published in local Long Island, New York newspapers such as The South Side Signal and The Hempstead Inquirer.

He also published a well-reviewed book about his travels to India, China, and Japan in the late 1880s, entitled Letters From The Far East.

DeLancey Floyd-Jones was also related (through direct line or marriage) to William Floyd and Philip Livingston, both signers of the Declaration of Independence; writer James Fenimore Cooper; John Loudon McAdam (creator of the road construction style named after him); Daniel Webster, Governor DeWitt Clinton of New York, Edith Wharton, and Alexander Hamilton.