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. ==Death==