Bamber was active in Liverpool and nationally for the best part of fifty years, present at key moments in Merseyside labour history, in the forefront of several prominent disputes. As a Labour councillor and a Justice of the Peace she promoted the dissemination of contraceptive advice as a mechanism to empower women.
Privately educated and living in one of the most affluent parts of that Edinburgh, Mary’s early life was very different from that of the poor in Liverpool she was ultimately to live among. However, when still a girl, her lawyer father took to the drink and one day walked out on the family never to be seen again. Her mother Margaret Little’s life up until then had been poor preparation for the rigours of single motherhood with six children to provide for. She worked hard charring and in other jobs to support her family, making a close acquaintance with near destitution and, when her eldest son got a job with a printer in Liverpool, the family came with him.
During the winter of 1906-7, Mary was on the rota of women who made soup to sell at a farthing a bowl from a Clarion caravan parked by St. George's Hall on Lime Street. She visited the sick, collected for the unemployed and kept open house for travelling socialists. She frequently spoke at outdoor meetings, often at the Wellington monument or on street corners. Sylvia Pankhurst described her as the "finest, fighting platform speaker in the country". In a city that was dominated by sectarianism, she refused any religious identification and was a regular heckler at both Catholic and Protestant political rallies.
However, it was through her work as a trade union organiser that Bamber became most visible. In the years leading up to the First World War, she worked tirelessly as an official for the Warehouse Workers Union. She travelled the length of the dock road, organising women from Johnson’s Cleaners and Dye Works in the North end to Wilson’s Bobbin Works in the South.
Bamber was often up before dawn to catch bag women - who made and mended the millions of sacks used to contain and transport the products which passed through the port - as they walked to work. Like employment in rope manufacture, which also drew Mary’s attention, this was heavy, filthy, poorly paid work often undertaken by only the most desperate – women caring for dependents, married women or those old and single. Mary gave a great deal of time - often fruitlessly in terms of actual recruitment - to talking to these women, pressing leaflets on them and persuading them to come to meetings.
Though her work as a trade union organiser was central to Bamber's politics, it was interwoven with other activity. She was present at the 'Bloody Sunday' demonstration during the 1911 Liverpool General Transport Strike. In 1919, she stood as the Labour Party candidate in the Protestant stronghold of Everton. Campaigning on everyday issues such as milk, education and municipal laundries, she won by a tiny majority. The same year, she became a founder member of the local Communist Party and in 1920 she attended the Second Congress of the Third International in Moscow. She was a local committee member on the National Unemployed Workers Committee and, in September 1921, was one of those arrested at the occupation of the Walker Art Gallery. She did not seek a second term as city councillor and by 1924 she had left the Communist Party, saying that it interfered with her work as an organiser. She was present at all the key demonstrations held during the 1920s and into the thirties. She spoke at her last meeting just two weeks before she died.