[5][6] Mercy Obiero made her international debut at the 2002 Commonwealth Games in Manchester where she failed to get a result in the 48 kg weight class.
[7] Four years later, she participated at the Commonwealth Games in Melbourne, where she finished in seventh place in the 63 kg weight class.
Obiero finished 13th in the 69 kg category, but later was moved up to 11th position (last among completed lifters), due to disqualifications.
[11] By competing in London, Obiero was the first Kenyan woman weightlifter at the Olympics and the second from Africa after Uganda’s Irene Ajambo.
[12] At the 2014 Commonwealth Games in Glasgow, Obiero finished in eighth place in the women's 69 kg weight class.