Joseph Deng was born in a refugee camp in Kenya after his mother left South Sudan to escape war. At age six his family moved to Australia, settling in Toowoomba and ran his first race aged nine. Aged 12, he moved to Ipswich in 2010 and attended Raceview State School. A school mate encouraged him to attend after-school athletics coaching at Ipswich Grammar. There he meet his first coach Di Sheppard who nurtured his talent. Also, key in his development was uncle John Deng, who he lived with at Redbank. Over the next five years he developed under Di’s coaching and support from the school in the form of a scholarship. By his late teens he was already running quick times. He was selected in the Australian team for the 2016 World Juniors and on tour, while still 17, he clocked 1:47.90 for 800m. He just missed making the final at the World Junior Championships placing third in his semi. He closed his junior years with a PB of 1:46.51.
He started strongly in 2018 with two 1:47 runs. At the National Championships/CG trials he faced the challenging 800m progression to the final of only the five heat winners and fastest three non-winners. He was drawn in Luke Mathews’ heat - the favourite for the event. He ran a good time of 1:47.52 and placed second, but was unfortunately the fourth fastest non-winner, meaning he missed qualification for the final. He did however qualify for the B final. He ran from the front to win by nearly two seconds in a significant PB of 1:45.71. It was also a CG A qualifier and faster than Mathews won the A race. A week later, the selectors named the teenager as the third athlete in the 800m for the Gold Coast Commonwealth Games.
Deng set his personal best at the 2018 Stockholm Diamond League when finishing second to training partner Peter Bol.
His hobbies are basketball and soccer. He is now coached by Victorian Justin Rinaldi who guided Alex Rowe to run 1:44.40, equalling the Australian record.