Daniel Willard was born on January 28, 1861 in Hartland, Vermont, the son of Daniel Spaulding Willard and Mary Ann Daniels Willard, farmers. In 1878, he entered the Massachusetts Agricultural College in Amherst, but problems with his eyesight prevented him from finishing his studies there. After he left, he found a job as a track laborer on the Central Vermont Railroad, beginning a career in railroading. He became president of the Baltimore and Ohio Railroad (B&O) in 1910.

His on-train service included positions as fireman, brakeman, engineer and conductor, while his on-ground service included stints as an agent, tower operator and engine house foreman. Willard quickly moved into the white collar ranks, and served as a trainmaster, assistant division superintendent, assistant general manager, purchasing agent, and operations vice president.

Willard began his career on the Vermont Central, followed by four years on the Connecticut and Passumpsic, one year on the Lake Shore and Michigan Southern, fifteen years on the Minneapolis, St. Paul and Sault Ste. Marie (Soo line), two years on the B&O, three years on the Erie and six years on the Chicago, Burlington, and Quincy.

His introduction to the B&O occurred in 1899, when he was brought to Baltimore by his boss on the Soo, F.D. Underwood. Underwood was hired as the general manager of the B&O, and tapped Willard to be his assistant general manager. Although Willard and Underwood left the B&O in 1901 when Underwood accepted the presidency of the Erie Railroad, this experience laid the groundwork for Willard's presidency of the B&O, which began in 1910.

Willard served as B&O president until April 30, 1941, the longest tenure of any B&O president. He oversaw the railroad during the challenging days of government supervision during the first World War, and the Depression. His service to the railroad industry also included the presidency of the American Railroad Association, 1911-1913, and the chair of the advisory commission of the Council on National Defense, where he was instrumental in the formation of the Railroad War Board. The Railroad War Board's function was to coordinate steam railroads for war purposes, and its plans, largely designed by Willard, remained in effect until the federal government took over the railroads on December 28, 1917.

It was through his work with the Council on National Defense that Willard became entangled with a mission to Russia in 1917 to aid work on the Trans-Siberian Railroad. Documents relating to the initiative form the series "Stevens Commission."

During the Depression, Willard negotiated a ten per cent across the board pay cut for railroad workers in an effort to avoid layoffs.

The Johns Hopkins University also benefitted from Willard's advice and business acumen. He was appointed as a trustee in 1914, and served as chairman of the board from 1926-1941. While on the board, Willard chaired a joint committee of the university and hospital boards whose goal was to design a fifty-year program for the development of both institutions. One of the group's most notable proposals was the establishment of the Wilmer Eye Institute.

Daniel Willard died on July 6, 1942, after a six week illness.