Minerva worked in the Department of Magical Law Enforcement at the Ministry of Magic for two years after graduation.
Dissatisfied with her job at the Ministry, in December 1956, Minerva returned to Hogwarts School of Witchcraft and Wizardry this time not to learn but to teach Transfiguration, under the head of department, Albus Dumbledore and later replaced him as Head of Department after he ascended to the position of Headmaster of the school.
As a teacher, Minerva was a strict disciplinarian, maintaining control of her students with a stern hand that made her someone not to be crossed and would, later on in her career, also be appointed the position of Head of Gryffindor House, the house in which she used to reside whilst studying at Hogwarts.
Albus Dumbledore would later on in his career also trust her enough to allow her to become Deputy Headmistress of the school and fill in for him on the occasions of his absence.
Her lessons as Transfiguraion Teacher consisted of, but were not limited to, match to needle, animal to water goblet, Beetle to button, and mouse-to-snuffbox transformations, as well as Vanishing, Conjuring and Switching Spells.
Through her early years at Hogwarts, Minerva remained close friends with her former boss, Elphinstone Urquart. During one visit, he proposed marriage to Minerva at Madam Puddifoot's Tea Shop. Surprised and embarrassed, and still in love with Dougal, she declined. Elphinstone, however, had never ceased to love her, nor to propose every now and then, even though she continued to refuse him.