In 1854, Hannah Cullwick met Arthur Munby during one of his regular urban expeditions to investigate working women. Munby was struck by her size (5 feet and 7½ inches (171.45 cm), 161 pounds (73 kg)) and strength, combined with the nobility of character he claimed to see in working women. Cullwick saw him as an idealised gentlemen, who celebrated the intense labour she did as a maid of all work. To be near Munby, she began to work in various middle-class households in London, including an upholsterer's, a beer merchant's, and that of a widow with several daughters, and in lodging houses (which gave her more freedom from supervision). She and Munby formed a lasting relationship, which led to a secret marriage in 1873.
Cullwick proudly called herself Munby's "drudge and slave", and called him "Massa", in a Master/slave relationship. For much of her life, she wore a leather strap around her right wrist and a locking chain around her neck, to which Munby had a key. She wrote letters almost daily to him, describing her long hours of work in great detail. She would arrange to visit him "in [her] dirt", showing the results of full day's cleaning and other domestic work. She had a particular interest in boots, cleaning hundreds each year, sometimes by licking them. She once told Munby that she could tell where her "Massa" had been by how his boots tasted.
Despite her display of subservience and loyalty, Cullwick remained independent. She stood up for herself if she thought the terms of her relationship with Munby were being violated. It was reluctantly that she entered marriage with Munby, seeing it as dependency and boredom. Once they were married, she moved to his lodgings in Fig Tree Court, Inner Temple, central London, where she lived as his servant, though she sometimes played the role of his wife. She also retained her own surname and insisted that Munby continue to pay her wages, and she had her own monetary savings. She left him far more often than he left her, and in 1877 she returned to domestic service in Shropshire. Munby was a regular visitor from 1882 until her death.