William Henry Mabury was born on October 18, 1841, in Pownal, Maine, to Charles and Martha Mabury. His father worked as a laborer. The family moved to Boston, Massachusetts, around 1846, and Mabury grew up there. He enlisted in the Union navy around June 18, 1861, and he served as an ordinary seaman. According to his military records, he was 5 feet, 4½ inches tall, with light hair and blue eyes.
He was admitted to the naval hospital at Norfolk, Virginia, on August 27, 1862, for typhoid fever, and he remained there until December 25, 1862. He fell ill again in February 1863, but he recovered after one week. He was discharged on June 17, 1863.
He returned to his parents’ household in Boston after leaving the navy. By 1870, he was a “master mariner,” and he owned $1,500 of personal property. By 1880, he was working as a tow boat captain. He applied for a federal pension in the early 1900s, suffering from heart disease, rheumatism, kidney disease, impaired vision, and “senile debility.” He secured a $6 monthly pension in 1904, and he received a series of increases over the next twelve years. By 1926, he was receiving $30 per month. He died in Boston on February 26, 1926.