As of my knowledge cutoff in September 2021, the record for the most Grand Slam singles titles in women's tennis is held by Margaret Court. She won a total of 24 Grand Slam singles titles throughout her career, which spanned from the 1960s to the early 1970s. Court's remarkable achievements include multiple victories at the Australian Open, French Open, Wimbledon, and US Open, solidifying her as one of the most successful players in the history of women's tennis.