Mary Wacera Ngugi (born 17 December 1988) is a Kenyan long-distance runner who competes in road running events. She holds personal bests of 66:29 minutes for the half marathon, 30:50 minutes for the 10K run, and 2:27:36 for the marathon. As a junior, she was a 5000 metres bronze medallist at the 2006 World Junior Championships in Athletics and the 2007 African junior champion. She is the widow of Samuel Wanjiru, the 2008 Olympic champion in the marathon, and had a daughter with him in 2010.