Sarah Jane Baines (30 November 1866 – 20 February 1951) was a British-Australian feminist, suffragette and social reformer. She was the first suffragette to be tried by jury, and one of the first hunger strikers. She was known as 'Jennie Baines' in the suffragist movement.

Sarah Jane Baines was born in Birmingham, England, in 1866 to Sarah Ann (née Hunt) and James Edward Hunt, a gun maker. She began work at Joseph Chamberlain's ordnance factory at the age of eleven. At age fourteen, Baines joined her parents in working with the Salvation Army. Upon attaining the rank of lieutenant at age twenty, she was sent to work as an evangelist in an independent working men's mission in Bolton. In this role, she was also called upon to act as a police court missionary caring for women who had been arrested.

On 26 September 1888 in Bolton she married George Baines, a boot and shoemaker, and the couple had five children between 1888 and 1899 three of whom survived childhood. Between motherhood and her work as a sewing machinist, there was little time for public activities. Yet Baines' commitment never wavered, her youngest surviving child was six years old when she was imprisoned for the third time. Annie Kenney called her 'one of the most kind-hearted woman one could meet, a born revolutionary'. Baines also joined the Independent Labour Party, the feeding of school children committee and the unemployed committee.

In October 1905, Baines read about the arrest of suffragists Annie Kenney and Christabel Pankhurst for assault and this motivated her to join the Women's Social and Political Union. Initially this was as a voluntary basis but in February 1908, Baines was made a paid organiser on a wage of £2 a week, organising open-air rallies, disrupting meetings and establishing new branches of the WSPU in the North of England and the Midlands.

Later this same year, in November 1908, Baines was to be tried of unlawful assembly at the Coliseum in Leeds, the first ever member of the WSPU to be tried by jury. Refusing to be bound over, she was convicted to six weeks imprisonment in Armley Goal, Leeds because "she did ‘not recognise the laws of this Court administered by men".

One of the first to advocate militant methods, Baines was imprisoned some fifteen times for her part in protests. In July 1909 with twelve others, including Mary Leigh, Lucy Burns, Alice Paul, Emily Davison and Mabel Capper and another in her wheelchair [May Billinghurst perhaps] she was jailed for obstruction for trying to stop Lloyd George's public budget meeting in Limehouse. The protest was witnessed by Annie Barnes who was inspired to join the East London Federation and influenced by Sylvia Pankhurst. On the way to Holloway prison the women arrested had shouted and sung protests and demanded to be treated in 'first division' in their own clothes as 'political' prisoners rather than criminals, this was not granted and the women broke 150 panes of glass at the prison and refused to give their names, prison officers had to use 'force necessary' to get the women into prison clothes. In Liverpool, in 1910, Baines was making speeches with Ada Flatman and Patricia Woodlock, when she was interrupted by Constance Lytton disguised as 'Jane Wharton' a seamstress asking 'the men and women of Liverpool to be the first to wipe out the stain [of force-feeding]' and a crowd followed them to the prison Governor John Dillon's house, chased by police.

In July 1912, Baines was part of an attempt, under the name 'Lizzie Baker' along with Gladys Evans and Mary Leigh and Mabel Capper, to burn down the Theatre Royal in Dublin the night before a scheduled visit from then Prime Minister, H.H. Asquith, to speak on Home Rule. For this Baines was sentenced to seven months hard labour and Central Bridewell prison, Dublin. Joining her fellow suffragette prisoners on hunger strike, she was released after five days.

The next year, on 8 July 1913, with her husband George and son Wilfred, Baines was accused of attempting to bomb first-class railway carriages at a Lancashire and Yorkshire railway siding, and leaving suffragist material, near where they lived in Manchester. A bomb, loaded revolver, masks and cutting tools and two catapults were found at their premises. As a result, her husband and son were charged with malicious damage and not imprisoned, but Baines was re-arrested under the 'Cat and Mouse act' and imprisoned at Holloway Prison. She again went on hunger strike, refusing food and water, and was released in a 'very serious condition'.