Theresa Garnett was born in Leeds in 1888. She was educated at a convent school and later became a teacher. After hearing Adela Pankhurst speak she joined the Women's Social and Political Union (WSPU).
In April 1909 she chained herself to a statue in the Central Lobby of the House of Commons, as a protest against a new law that penalized anyone found guilty of disorderly conduct within the confines of the Palace of Westminster while parliament was in session.
On 27th June 1909 Garnett was arrested during a demonstration outside the Houses of Parliament that resulted in her throwing stones in Whitehall. She was sentenced to a month in Holloway Prison. Garnett immediately went on hunger-strike. She was then accused of biting and kicking a wardress. She was found guilty of assault and sentenced to a further term of imprisonment.
Garnett continued to take part in militant activity and in August 1909 she took part with Mary Leigh, in a demonstration on the roof of the Sun Hall in Liverpool. She was imprisoned in Walton Prison, but after going on hunger-strike she was released later that month.
In November 1909, she accosted Winston Churchill with a whip. She shouted "take that you brute", however, she later admitted she missed him. She was arrested for assault but was found guilty of disturbing the peace. Garnett was found guilty and was sentenced to a month's imprisonment in Horfield Prison. Her friend, Mary Blathwayt, wrote in her diary on 15th November: "Miss Garnett got one month for whipping Mr. Churchill across the face and not hurting him. I bought fruit and sent it to the prisoners before they were taken away."
The following day, her mother, Emily Blathwayt, wrote: The papers were full of Saint Theresa as we call her." Emily went onto say that the movement was "not altogether displeased" that the newspapers had headlines that were not true such as "Winston whipped" and "Churchill flogged". Emily added that her husband Colonel Linley Blathwayt had "sent her photo which he had taken by Mary who gave it to her before she went off to prison."
Theresa Garnett went on hunger-strike while in Horfield Prison. This time, instead of being released, she was forcibly fed. As a protest against this treatment, she set fire to her cell and was then placed in solitary confinement for 11 of the 15 remaining days of her sentence. After being found unconcious, she spent the rest of her sentence in a hospital ward.
In 1910 Garnett became WSPU organizer in Camberwell. However, she disagreed with the WSPU arson campaign and left the movement. According to Elizabeth Crawford, the author of The Suffragette Movement (1999) she "did not join any other suffrage group, although she obviously kept in touch with her erstwhile comrades."
Theresa Garnett died in 1966.