Having worked in his youth as a log driver on the Mississippi River,[1] Mathieu came to Rainy River from Minnesota around 1903 as a manager of the Rainy River Lumber Company's sawmill, later becoming manager and vice-president at the Shevlin-Clarke Company.[4] He was later involved in controversy as part of what became known as the "Old Tory Timber Ring,"[5] when fellow Conservative Howard Ferguson, as Minister of Lands and Forests, arranged for the sale of three timber limits in the Quetico Forest Reserve to Shevlin-Clarke for less than half the price they would have normally fetched,[6] and the company later paid a fine of $1.5 million for breaching the Crown Timber Act.[7] The transactions were criticized in a subsequent inquiry.[8]
In 1921, he left Shevlin-Clarke and founded J.A. Mathieu Limited, which set up a mill at Rainy Lake.[9] The company opened another sawmill in 1945 at Sapawe Lake, near Atikokan.[10][11] He was instrumental in pioneering the use of mechanized equipment in the woods (while other firms were still relying mainly on horses), as well as in using aircraft.[12] After his death, the company was acquired by Domtar.[11]
He set up an educational foundation to provide financial assistance for students from the area,[12] for which he was honoured in 1958 by the Ontario Secondary School Teachers Federation.[2] Mathieu also established a wildlife reserve and help fund community projects in the region.[12] During his time in the provincial assembly, he helped promote the development of roads to encourage settlement in the district.[12] He also served as President of the Northern Pine Manufacturers Association for 22 years.[2]
