Hedwig Weitzel was born in Palmerston North on 17 September 1900, the daughter of German parents Marie Benninghoven and her husband, Friedrich Gustav Weitzel, a brass founder. The family subsequently moved to the Horowhenua area and by 1912 were living in Wellington. Hetty attended Wellington Girls' College from 1914. The First World War years were difficult: a German name was not an asset. Although she was New Zealand-born and her father had been naturalised in 1902, she was sent from class when the war was discussed. At home her parents encouraged critical thought and free discussion. They were socialists and anti-militarists, and their home in Buller Street was a gathering place for militants. Following Friedrich's death in 1917, Marie Weitzel took in boarders, many of whom were part of this radical sub-culture.
On leaving school Hetty studied philosophy and economics at Victoria University College. She completed a BA in 1920 and during 1921 was enrolled at the Teachers' Training College, Wellington. On 2 April that year she joined the Wellington branch of the revolutionary New Zealand Socialist Party, to which her mother and other family members already belonged. At another meeting on 10 April the branch resolved to transform itself into the Communist Party of New Zealand (CPNZ); Weitzel became a founding member and literature secretary for Wellington.
As part of her duties she sold communist literature from the party headquarters in Manners Street. On 19 June 1921 she sold a copy of the Communist, an Australian journal, to a policeman posing as a CPNZ member. She was arrested and on 19 August appeared in the Magistrate's Court charged with selling seditious literature. She pleaded not guilty on the grounds that she did not know the journal was banned, but was convicted and fined £10. Soon after her conviction she was expelled from the Teachers' Training College.
Hetty Weitzel became the talk of Wellington; questions were asked in Parliament, and when a group of students contributed to her fine the minister of education, C. J. Parr, initiated an inquiry into the influence of communism in the teachers' college and the university. Despite finding little evidence of radicalism, Parr introduced a loyalty pledge for New Zealand teachers. He also called for a public inquiry into the conduct of a teacher, Jean Park, who had written a letter to National Education protesting against Weitzel's dismissal. He was restrained, however, by a Supreme Court injunction granted to Park and the New Zealand Educational Institute.
With no prospect of continuing in her chosen profession in New Zealand, Weitzel moved to Sydney in February 1922. She completed her training, and remained teaching until her retirement in about 1960. Despite keeping in touch with New Zealand friends, especially the trade union leader F. P. Walsh, she spent the remainder of her life in Australia.
In Sydney she joined the Communist Party of Australia (CPA), gaining office in the Sydney branch and sitting from 1922 to 1929 on the party's central committee. Responsible for the youth section of the party, she edited the Communist's monthly supplement, the Young Communist, and also taught at the communist Sunday school. Through this work she met Hector Ross, a builder's labourer, who was also a member of the CPA central committee. The couple were married in Sydney on 15 December 1923. They visited New Zealand for several months from December 1924 to help reorganise the CPNZ. As a result the party was temporarily dissolved and reformed as a New Zealand section of the CPA.
Back in Australia Hetty worked with Hector editing the CPA paper, the Workers' Weekly, taking charge for a while in 1926 when he was overseas. That year she became leader of the CPA women's section, later known as the Militant Women's Group. She was the principal author of the 1927 party programme Woman's road to freedom in which she advocated equal pay and a child endowment. In 1929 she separated from Hector and reverted to her family name. Temporarily leaving Sydney, she taught mathematics at Cowra high school and in October 1931 she and Hector were divorced. They had no children.
In the 1930s Hetty Weitzel helped edit Working Woman and its successor, Woman To-day. However, several new women had come into prominence within the CPA, among them fellow New Zealander Jean Devanny, with whom Weitzel did not always agree. By the late 1930s she was putting most of her energy into the Australian Teachers' Federation, of which she was an executive member for 30 years. From 1936 she chaired a federation committee on equal pay and in 1939 served again on the CPA central committee.
In her last years Hetty Weitzel suffered from Parkinson's disease. She died in Sydney on 26 October 1971. In Australia she is considered a role model for a generation of communist women radicalised in the late 1920s and 1930s. In New Zealand she is remembered for selling 'naughty books'.