Kathleen Yardley was born in Newbridge, County Kildare, Ireland, the daughter of a postmaster. Her family moved to England when she was five years old. She attended Ilford County High School for Boys in order to learn math and science because the local girls' school didn't offer the subjects. She went on to study physics and mathematics at Bedford College in London in 1919. After graduating, she earned an MSc in physics from University College London (UCL), where she joined the research team organized by noted crystallgrapher William Bragg. In 1927, she married Thomas Lonsdale and the couple had three children. Kathleen Lonsdale worked at the University of Leeds and then moved to the Royal Institution (RI). She was awarded a doctorate from UCL in 1936 while working at the RI. After World War II, she was appointed as reader in crystallography in the Chemistry Department of UCL. She was a pioneer in the use of X-rays to study crystals. Her main contribution was the discovery of the structure of benzene and hexachlorobenzene, and her work on the synthesis of diamonds. In 1949, she became a professor of chemistry and head of the Department of Crystallography at UCL. She was the first tenured woman professor at that college, a position she held until 1968, when she was named professor emeritus. She was one of the first women to be elected a Fellow of The Royal Society in 1945 and was the recipient of their Davy Medal. She was appointed Dame Commander of the British Empire by Queen Elizabeth II in 1956. Dame Kathleen Lonsdale and her husband were both committed pacificists who joined the Quakers in 1935. She wrote several books about peace and war in addition to her scientific publications. A rare meteoric diamond was named Lonsdaleite in her honor.