Helen McKenzie Murray was born in Aberdeen, Scotland, on 16 August 1896. She was the daughter of Helen McKenzie and her husband, Alexander Innes Murray, a shipmaster with the Shaw Savill and Albion Company. Before Helen was a year old, the family came to New Zealand to join Alexander, whose ship was laid up in Lyttelton; they eventually settled there. Helen later attended Lyttelton West School and Christchurch Girls' High School. Her autobiography refers to a fiancé killed on the battlefields of France, and to her early career as a clerk, during which she found 'solace in hard work'. She apparently sought solace of a different kind in marriage to a Royal Navy lieutenant commander, Leslie Douglas Stuart Murray, at Lyttelton on 3 January 1921. However, the marriage lasted little more than three years before the couple divorced; they had no children. It is an indication of the social stigma attached to divorce in the 1920s that Helen's autobiography makes no reference to the marriage or its ending.
It was Helen's second marriage, to Robert Sheriff Black, at Dunedin on 3 December 1924, which she clearly regarded as a turning point in her life. It certainly added to her social status. Robert was a prominent fur merchant and exporter, nearly 30 years Helen's senior, with adult sons of her age. In 1927 he was re-elected to the Dunedin City Council, and in 1929 he became Dunedin's mayor. In the meantime, however, the couple went on a year-long world tour, after which their first child, a son, was born in 1927. The couple were subsequently to have another son and two daughters.
Helen Black later expressed her trepidation at becoming mayoress, given her inexperience of public life and her family responsibilities. She had cause for concern, since her conservative husband's term of office coincided with the onset of the depression and the couple's behaviour did not endear them to the unemployed. Helen participated fully in Dunedin's social life, sponsoring gala occasions intended to raise community spirits and promote the city. She also involved herself in good works: organising picnics and Christmas parties for the children of the unemployed, and running the St Andrew Street relief depot.
Although well-intended, it was this last activity which brought Black into conflict with unemployed men and their families. She gained a reputation for behaving as a 'grand lady', wearing gloves while dispensing aid to the poor. When tensions came to a head in April 1932, the mayoress's depot was the target of demonstrations. Helen Black, who had refused to distribute aid unless applicants agreed to be investigated, tried to remonstrate with 'these people'. She was terrified when the crowd responded by smashing windows in the depot and attempting to overturn her taxi as she departed. Threats to attack her home and kidnap her small daughter made her regret she had ever become mayoress. In later years she was to make a more generous assessment of the situation: 'I find it hard now to criticise the unemployed for their disturbances. I wonder how those of us who had sheltered homes and work to occupy our minds, would have acted had we been in their position?'
Robert Black lost the mayoralty in 1933. However, Helen developed political aspirations of her own, and stood as a Democrat Party parliamentary candidate during the 1935 election. Her laissez-faire pro-business stance went against the tide of voter sympathies at that time, but her platform did show a commitment to women's issues and to such concerns as public health, the purity of food supplies and prison reform. She also had strong views on the need for monetary reform, having been influenced by opinions put forward by the women's magazine Mirror.
Robert died in 1939, when their youngest child was only one year old. Helen then added management of the family firm and business trips overseas to her formidable list of activities. Involvement with the Women's War Service Auxiliary followed. She acknowledged, however, that wartime difficulties in obtaining domestic help and the marriage of her sister, who had for many years run the Black household, made life 'rather difficult in every way'. As a way of coping, she sent her children to boarding school and continued with her other duties.
Loss of her deposit in the 1935 election did not deter Black from standing again for Parliament, as a New Zealand National Party candidate in 1954, but once again she was unsuccessful. Throughout her life she achieved more by working on the local scene in such organisations as the National Council of Women of New Zealand, the Navy League, the Travel Club, the Dunedin Repertory Society, the Otago Women's Club, the Otago Girl Guides Provincial Association, and the Townswomen's Guild (which she inaugurated in Otago in 1939). She published her autobiography in 1947. Helen Black's contribution to the community was recognised by her being appointed an MBE in 1952. On 6 July 1960 she married Stanley George Bennett, a tea planter, in Croydon, Surrey. She died of cancer in Christchurch on 17 October 1963, and was survived by her husband and four children of her second marriage.