Niz qualified for the men's 4×200 m freestyle relay, as a member of the Portuguese team, at the 2004 Summer Olympics in Athens. Teaming with Luís Monteiro, João Araújo, and Miguel Pires in heat one, Niz swam a second leg in a split of 1:52.35, but the Portuguese team settled only for seventh place and fourteenth overall with a national record of 7:27.99.