After securing her first teaching assignment, Mary Harris permanently left Canada, never to see her family again. Harris settled in the United States and started to teach at a convent school in Monroe, Michigan. Although Harris was raised as a Roman Catholic, she was hired because of her ability to teach secular subjects. However, after only a few months of teaching, Harris left Michigan for Chicago in early 1860. She worked as a dressmaker, putting to use the skills that she had developed while growing up. Harris did not stay long in Chicago, and before the end of the year, she had already moved to Memphis, Tennessee, where she began teaching again.
In the 1850s, Memphis became a growing metropolis, as railroads expanded and its location made the city a significant economic center. With this expansion came many immigrants, a large part of whom were Irish. In Memphis, Harris met George Jones, who she married in 1861. Since George's job as an iron molder, which a highly skilled trade, ensured economic stability for him and his wife, Harris left her job to stay home and raise her family. George Jones worked for the Union Iron Works, where he participated in one the early union movements within the United States. Mary Harris was not yet directly involved in the American labor movement, but she probably read the pamphlets and journals that George Jones brought home.
Harris lived a stable life taking care of her four children: Catherine, Elizabeth, Terence, and Mary. In 1867, however, economic troubles resulted in cuts in wages and rising unemployment, and a yellow fever epidemic began to sweep through Memphis. The people who had the means to escape from the city did so, but the Jones family had no other alternative but to stay. Yellow fever was a deadly and fatal disease. Painful death followed a few days of hemorrhaging, vomiting of blood, jaundice, and liver failure. Many Memphis residents died, among them all four of Harris's children. Finally, George Jones also died, leaving Harris all alone. George Jones's union collected money for Harris. She began to help other people, and to nurse those who were sick. When the epidemic was over, Harris left Memphis to start a new life in Chicago.
Relying again on her skills as a dressmaker, Harris established a business that brought her into frequent contact with the wealthy classes of Chicago. After only a few years, Harris's life was again disrupted, as the Chicago Fire of 1871 swept through the city, destroying her home and all of her belongings. Like other workers, Harris took part in the rebuilding of the city. During the 1870s, she also began to be more involved with the labor movement. In 1877, strikes against the railroads occurred nationwide as workers expressed their dissatisfaction with wage cutbacks. Sympathy strikes spread, and were met with violence and repression. During the 1870s and early 1880s, organizations such as the Knights of Labor started to gain greater influence by organizing laborers of different trades. The Working-Men's Party had developed into the Socialist Labor Party, and even held a few elected offices in government. People were receptive to new political ideas such as socialism and anarchism. In Chicago, the anarchist movement was particularly strong, with a strong following among the immigrant populations. Fighting for an eight-hour day, labor organizations planned a massive strike for May 1, 1886. The walkout was peaceful, but during the following days, violence erupted at Haymarket square. An anarchist meeting had been taking place peacefully, when someone threw a bomb at approaching policemen. Police shot into the crowd, killing an undetermined number of people. The official response to the Haymarket Tragedy was to convict eight anarchist leaders for their militant rhetoric, sending some to the gallows. There was no proof that they had been involved, but the sentence was carried out despite international protest, and four of the suspects were hanged. Those who remained in jail were later pardoned by the governor of Illinois. Harris was definitely influenced by the Haymarket incident, and it fueled her determination to fight for the working people.
In her autobiography, Harris does not go into detail about her life with George Jones or her children. Clearly, she suffered from their deaths, and tried to lessen her own pain by relieving the suffering she saw around her in the slums of Chicago. Her direct involvement in the labor movement came very gradually, and she even suggested at one time that her involvement came from the loss of her children and husband. Harris felt helpless as they died, particularly since the causes of yellow fever were not known at the time. Harris felt, however, that the causes of poverty were known and wanted to combat this exploitation in order to improve the lives of the laboring masses.