Hirshhorn went to work as an office boy on Wall Street at age 14. Three years later, in 1916, he became a stockbroker and earned $168,000 that year. A shrewd investor, he sold off his Wall Street investments two months before the collapse of 1929, realizing $4 million in cash. Hirshhorn made his fortune in the mining and oil business. In the 1930s, he focused much of his attention on gold and uranium mining prospects in Canada, establishing an office in Toronto in 1933.