Harriet Brooks was born on July 2, 1876 in Exeter, Ontario, Canada. She had eight brothers and sisters.
In high school, both Harriet and her sister Elizabeth were interested in science. When the girls graduated, they wanted to go to college - something that was not encouraged, and indeed was usually discouraged, for girls at that time.
Harriet applied to McGill University, in Montreal, Quebec. She was accepted, and given a scholarship. (Two years later, Elibeth would follow her.)
In 1894, Harriet was only one of a handful of female students at McGill. McGill had only issued a degree to a woman for the first time in 1888. Indeed, according to Canadian law, women weren't even "persons."
Harriet had to endure rudeness from some of her male classmates and instructors, but she persevered. By her third year, she was elected class president, and in 1898 she graduated with first rank honors in mathematics and a teaching diploma.
Harriet didn't want to be a teacher, however, she wanted to work in a laboratory as a researcher.