Catherine Anne Grant (Katie) Sadleir (born 14 August 1964 in Torphins, Scotland) is a former synchronized swimmer. She competed for New Zealand at the 1984 Summer Olympics in Los Angeles with her sister Lynette Sadleir. In the Women's Solo Katie finished 37th and in the Women's Duet Katie and Lynette finished 12th.
At the 1986 Commonwealth Games in Edinburgh Katie won the Bronze medal in the Women's Solo.
She was the Assistant Chef de Mission for the New Zealand team at the 1994 Commonwealth Games in Vancouver.