Born on Lower Grosvenor Street in London Louisa was the daughter of General Edward Bowater and Emilia Mary Barne. She was educated at home and kept a diary from the age of fourteen. The family were close to the British Royal Family, and Louisa was a Lady-in-Waiting at the marriage of Prince Leopold. In 1869, she married Knightley twenty-three years her senior.
Knightley devoted much of her time to the church, serving as a national vice-president and the Peterborough diocese president of the Girls' Friendly Society. She was also interested in politics, and when the Primrose League was established in 1883, she soon joined, and from 1885 until 1907, she served on its Ladies' Grand Council. In line with the organisation's aims, she was very active in mobilising women in support of the Conservative Party, and was credited with saving Rainald's seat in the 1885 and 1886 general elections. The experience of involvement in an election campaign without being able to vote convinced her of the case for women's suffrage.
Probably due to Louisa's lobbying, Rainald was created Baron Knightley in 1892. Rainald died in 1895, and Louisa thereafter devoted more of her time to women's rights. She was a founder member of the National Union of Women Workers, serving as a vice-president from 1906, also serving on the committee of the Freedom of Labour Defence League, and as president of the Northamptonshire Society for Promoting the Return of Women as Poor Law Guardians.