In his early career Ahearn worked as a telegraph operator and then became the Ottawa branch manager for the telegraph and telephone companies.
In 1882 he started an electrical contracting business with his partner, W.Y. Soper. The business grew and provided Ottawa with electricity, streetcars and street lights.
Ahearn displayed to Canadians a variety of electrically powered devices throughout the 1880s and 1890s.
In 1892 he prepared the first dinner cooked entirely with electricity, at the Windsor Hotel in Ottawa. Ahearn won the first gold medal ever awarded by the Central Canadian Exhibitions Association for excellence in exhibits.
Ottawa got its first electrically heated streetcar in the 1890s.
Sample of inventions patented in Canada by Ahearn
| Patent Number | Filing Date | Title |
| 17669 | 1883 | Fire Alarm Telegraph |
| 38976 | 1892 | Electric Water Heater |
| 39506 | 1892 | Electric Heater |
| 39507 | 1892 | System of Warming Cars by Means of Electrically Heated Water |
| 39508 | 1892 | Apparatus for Electrically Heating an Automatic Water Supply |
| 39916 | 1892 | Electric Oven |
| 39917 | 1892 | Electric Flat Iron |
