Lumpkin's first job was as a factory worker in 1933, at the age of 14; she lied about her age so she could get a fifteen-cent-an-hour position assembling radio tubes. Soon after, she wrote her first flyer titled "Are you satisfied?" and helped organize African-American laundry workers, in Harlem and the Bronx, who were paid low-wages during the Great Depression. She joined the Metal Workers Industrial Union, later part of the Congress of Industrial Organizations. While at Hunter College, she helped organize a student strike to protest American militarism in 1935, for which she was suspended from the school. She was suspended again two years later for putting together an antifascist student conference. She was also an organizer for the Laundry Workers Industrial Union and joined the Communist Party from an early age. In 1937, she was hired by the Congress of Industrial Organizations, along with 15 others, for a campaign to organize 30,000 laundry workers into a union. She also joined marches protesting the imprisonment of the Scottsboro Nine and the Italian invasion of Ethiopia.