In 1933, she began working in the clothing industry, and joined the Garment Workers' Union of South Africa (GWUSA).
By 1937, she was working as an organiser for GWUSA, and was also secretary of the Johannesburg Sweet Workers' Union.
[2] Hartwell worked closely with Solly Sachs, the general secretary of GWUSA, and the two married in 1942.
Hartwell next became secretary of the clothing industry unemployment fund, then its medical aid society.
[3] That year, she became general secretary of the South African Trades and Labour Council, then of its successor, the Trade Union Council of South Africa, which excluded black workers.