Ngouabi competed only in the men's 100 m freestyle at the 2000 Summer Olympics in Sydney. He received a Universality place from FINA, in an entry time of 59.50. He challenged six other swimmers in heat two, including 15-year-olds Ragi Edde of Lebanon and Dawood Youssef of Bahrain. He pulled himself farther from the top field to a sixth seed in 1:00.39, almost a full second below his entry standard and 6.84 seconds behind leader Gregory Arkhurst of Côte d'Ivoire. Ngouabi failed to advance into the semifinals, as he placed sixty-eighth overall in the prelims.