Mitchell worked as a delivery woman and babysitter while attending segregated public schools in Richmond. Nonetheless Mitchell graduated at the very top of her class in 1883. She then taught grade school for three years at the Lancaster School, and at the same time she took classes in accounting and business. Mrs. Walker became an important community organizer for the Independent Order of St. Luke, a fraternal burial society that provided humanitarian services to the elderly. In 1902, Walker started a newspaper for the St. Luke organization called the St. Luke Herald. After the success of the newspaper, she started the St. Luke Penny Savings Bank and became the first woman in the United States to charter a bank. She was also the bank’s first president. During the Great Depression two other banks in Richmond merged with St. Luke to become The Consolidated Bank and Trust Company which continues to be the oldest black-owned and black-run bank in the United States.
Walker went to work with remarkable energy and showed considerable business acumen. In 1902 she founded the St. Luke Herald to carry news of the order to local chapters and to help in its educational work. This included information regarding the training of children in habits of thrift, industry, and hygiene. In 1903 she opened the St. Luke Penny Savings Bank, of which she was president. By 1924 the main office staff of the order had grown to 50 individuals who served a membership of more than 50,000 in 1,500 local chapters. From 1929 to 1930 the Penny Savings Bank absorbed all other banks in Richmond owned by African Americans and became the Consolidated Bank and Trust Company.