Having begun his career in his native country, Onyango went on to play in the South African Premier Soccer League with Supersport United, Mpumalanga Black Aces, and Mamelodi Sundowns. With Mamelodi Sundowns, he won the 2016 CAF Champions League and took part in the 2016 FIFA Club World Cup. He was named the 2016 African-based African Player of the year. He was also ranked as the tenth best goalkeeper in the world in list for 2016 compiled by the International Federation of Football History &amp; Statistics.