Darby Bergin was born in York (later Toronto), Upper Canada in 1826, the son of William Bergin, a York merchant who had immigrated from Ireland. He studied at Upper Canada College and McGill College, receiving his MD.CM in 1847. Bergin set up practice at Cornwall. He was founder and president of the Eastern District Medical Association, president of the St. Lawrence and Eastern District Medical Association and examiner for the College of Physicians and Surgeons of Ontario, also serving president of the council for the college from 1881 to 1882 and from 1885 to 1886. With his brother John, he also raised horses and cattle.

Bergin represented Cornwall from 1872 to 1874 and from 1878 to 1882 and then Cornwall and Stormont from 1882 to 1896 in the House of Commons of Canada as a Liberal-Conservative member. He was defeated by Alexander Francis Macdonald, the brother of Donald Alexander Macdonald, in 1874. He opposed the Canada Temperance Act of 1878, feeling that, in the end, it increased, rather than prevented, the consumption of alcohol. Bergin also introduced private member's bills to regulate working conditions for women and children, even though it was believed by some that labour regulations fell under provincial control; his efforts led to the introduction of legislation regulating labour conditions in Ontario factories.

With Joseph Kerr, he promoted the development of the Ontario Pacific Railway, serving as president from 1886 until his death in 1896, when his brother John succeeded him. Bergin also helped promote the expansion of the Cornwall Canal.

Bergin was very active with the Canadian Militia. He was appointed a Surgeon in the 3rd Battalion, Stormont Militia in 1850 and in 1851 transferred to the 4th Battalion. In 1862 during the Trent Affair, he raised and commanded the 1st Cornwall Rifle Company, which served on active duty as No. 3 Company, 3rd Provisional Battalion, in La Prairie from December 1863 to April 1864, and during the St. Albans Raid.

He commanded the company on active duty in Cornwall during the Fenian Raid in 1866, and when the 59th Stormont and Glengarry Battalion was created on July 3, 1868, Major Bergin was appointed the first Commanding Officer. He commanded the battalion in the garrison at Cornwall during the Fenian Raid of 1870, and remained in command of the regiment until 1885. He was succeeded by Colonel J.H. Bredin.

On April 1, 1885, Colonel Bergin was appointed to command of the medical services for the North-West Field Force that was mobilizing for service in the North-West Rebellion. He was appointed Surgeon General and served with Middleton's expedition in 1885. Although he was unsuccessful in persuading the government to create a permanent militia medical corps following the North-West Rebellion, the Royal Canadian Army Medical Corps was later established in 1904.

On October 22 1896, Darby Bergin died in Cornwall while still in office after succumbing to an unidentified illness.

On Mr. Bergin being unseated on petition, 24 December 1879:

• Biography at the Dictionary of Canadian Biography Online
• Darby Bergin – Parliament of Canada biography
• Darby Bergin fonds, Library and Archives Canada