Dominick J. O'Malley was born in New York City in 1867. His father, Dominick O'Malley, fought in the Civil War with New York's 69th Regiment and remained in the military in New York City after the war until he was transferred to Fort Concho near San Angelo, Texas, in December 1866. The elder O'Malley underwent surgery for the removal of a minie ball in New York in 1869, but died from the effects of the surgery in early 1870. D.J. O'Malley's mother, Margaret, remarried a soldier, Charles H. White, who was transferred to Fort Dodge, Kansas, in 1872, and then to Fort Larned, Kansas, in 1873. In 1875 White was discharged and traveled to Cheyenne, Wyoming Territory, where he secured work as a carpenter. The family joined White and moved soon thereafter to Fort Sanders near Laramie City, Wyoming, where White had enlisted in the Second U.S. Cavalry.

In September 1877, the White family moved to Fort Keogh, Montana Territory. White was discharged in 1881 and disappeared in the fall of that year never to be seen again by his family. Margaret White and her children moved to Miles City and Dominick started work as a horse wrangler for an officer named Logan, who ran cattle on the range near the Little Dry Creek. Logan was bought out in 1881 by the Niedringhaus brothers of St. Louis, Missouri, who ran the Home Land and Cattle Company, or, N Bar N. O'Malley worked for the N Bar N until 1896, when it was bought by McNamara and Marlow. Between 1881 and 1896 he drove cattle from Texas to Montana and worked in various capacities including horse wrangler, as part of the range crew, and as representative, or "rep", someone who worked the ranges outside the main range of the company.

After leaving the N Bar N, O'Malley worked for several outfits in eastern Montana, including the Bow and Arrow, the M Diamond, the Quarter Circle L, and the L U Bar. He also served as a special deputy sheriff in the town of Rosebud. From 1901 to 1904 he worked as a deputy inspector for the Montana Stock Growers Association. O'Malley then worked for two years for the Montana Cattle Company (the 79) on its Musselshell River ranges. In 1906 he was hired by the Keeline Brothers on Cabin Creek.

In March of 1908 the Montana State Prison hired O'Malley as a guard and he worked there until 1911, when he moved to Wisconsin where he was married in the same year. O'Malley lived in Eau Claire, Wisconsin, for the rest of his life, except for the period 1921 to 1923, when he returned to Montana to once again work as a guard at the state prison in Deer Lodge. In Eau Claire O'Malley operated a raspberry farm and worked at the Gillette Rubber Company (later UniRoyal) from 1927 to 1941. He died on March 6, 1943.

O'Malley started writing poetry in the 1880s and had many pieces published in the Miles City Stock Growers Journal in the 1880s and 1890s. He also wrote about events that he witnessed, which occurred during the time he lived in Montana. These were published in various newspapers, especially in Miles City and Eau Claire. Some of his poetry has been used as music lyrics. O'Malley and his wife Margaret had two daughters, Margaret and Alicia. O'Malley went by the name of his stepfather, White, until he moved to Wisconsin when he adopted the name of his biological father. During his cowboy days O'Malley was nicknamed "Kid White" and the "N Bar N Kid." He sometimes used these names as well as humorous names, such as "Jack R. Abbit" and "Iyam B. Usted" as his byline.