Mary Jane Lewis was born at Llanvaches, Monmouthshire, Wales, on 18 April 1852, the second daughter and third child of Hannah Morgan and her husband, Thomas Lewis. Hannah and Thomas, who owned a farm, both died before their children reached adulthood. It is thought that the farm was badly managed by trustees, and soon after Mary Jane's brother, Thomas Morgan Lewis, inherited the estate and a number of cottages he sold them. With his new wife and two sisters he made plans to emigrate to New Zealand.
The party arrived at Auckland, New Zealand, in October 1870 on the Asterope. While searching for a place to settle they arrived at Ngaruawahia. It was here that Mary Jane Lewis met Charles Innes, a Scotsman more than 20 years her senior. They were married on 30 April 1874 at Auckland. Charles Innes had established a brewery at Ngaruawahia some years earlier. However, a large mortgage and a small local population led to almost inevitable bankruptcy.
After their marriage the couple decided to shift to Te Awamutu. Mary Jane assisted Charles in financing a new brewery with money received from the sale of her parents' farm. It was evident she was creditworthy: property was registered in her own name from 1875 onwards. In 1875 the first of their 10 children was born and Mary Jane managed a large home opposite the brewery.
In October 1888 Charles Innes was declared bankrupt again. Soon afterwards Mary Jane Innes announced by public notice that she had taken over the management of the Te Awamutu Brewery, brewing ale and producing aerated waters. Showing considerable business acumen, in November 1889 she announced that she had taken over the management of the Waikato Brewery as well. This brewery had been established in Hamilton East in 1873 by William Cumming. The Innes family acquired tenancy rights over the land and buildings and shifted to Hamilton. The Te Awamutu Brewery was allowed to run down and Mary Jane and Charles concentrated their efforts on the Hamilton East business. Charles was the brewer: his products were popular and renowned for quality. An increase in the population of Waikato and improved economic conditions also helped considerably. But a disastrous fire in April 1897 virtually destroyed the brewery and aerated-water factory. Although the position seemed hopeless, Mary Jane refused to give up.
In 1877 Charles Innes had purchased a section in Hamilton West which he relinquished after a short venture bottling products from the Te Awamutu Brewery. The section was repurchased and Mary Jane Innes began to organise yet another brewery. By 1898 a new building was standing on the site where the well-known Waikato Brewery was later situated.
Setbacks were not over, for in July 1899 Charles died. It was at this time that Mary Jane most clearly displayed her strength of character and independence. She arranged a series of loans, paid off her late husband's debts and became the sole and uncontested owner of the Waikato Brewery, with an impressive list of assets. Her eldest son, Charles Lewis Innes, was then in an apprenticeship with the Great Northern Brewery in Auckland, and she came to rely on him. In 1900 she arranged a deed of partnership with her son and he became the manager of a new company named C. L. Innes and Company. A period of expansion began and for over 60 more years the company traded as a greatly respected and profitable local business. About 1907 or 1908 Mary Jane Innes shifted to Auckland, leaving the management of the brewery to Charles Lewis Innes and her other sons. She relinquished her shares in the company in 1912.
Mary Jane Innes overcame crises and disappointments in her life; she also encountered tragedy. Her sister Annie, with whom she had a close bond, died prematurely in 1878. She was widowed at a relatively young age. Of her eight sons and two daughters, only six sons survived to adulthood. The final blow came in 1918, when Charles Lewis Innes died in the influenza epidemic. Mary Jane Innes was grief-stricken at her favourite son's death. She lived to the age of 89, dying at Auckland on 14 November 1941, and was buried beside her husband in Hamilton East cemetery.