Western Eagles Deng made his senior football debut as a 16 year old in 2013 at
Western Eagles under then-manager
Srecko Barešić-Nikić in the
Victorian State League Division 3.
Green Gully The following season, the youngster moved to nearby
Green Gully, where manager Bob Stojcevski recruited Deng to play for the club's u20 side. He was eventually promoted to the senior team and made 13 first team appearances in the
NPL Victoria in 2014.
Melbourne Victory Following his impressive performances at Gully, Melbourne Victory National Youth League coach
Darren Davies rewarded Deng with a youth contract. Deng debuted for the senior team for
Melbourne Victory against
Balmain Tigers in the
2015 FFA Cup. He made his
A-League debut on 9 October 2015 against
Adelaide United, as a substitute replacing
Fahid Ben Khalfallah after a
red card was shown to
Leigh Broxham. Thomas made his starting debut in the
A-League for Melbourne Victory on 17 October 2015 in round 2 against
town rivals,
Melbourne City, where he was selected as Man of the Match by supporters and social media.
Jong PSV (loan) In June 2016, Deng moved to
Jong PSV on a one-year loan deal. After making five appearances, he returned to Melbourne Victory at the end of the season.
Urawa Red Diamonds On 28 January 2020, Deng left Melbourne Victory to join Japanese club
Urawa Red Diamonds following his wonderful performance at the
2020 AFC U-23 Championship. On 23 August in a league match against
Vissel Kobe, he scored a goal in a 2–1 lost.
Albirex Niigata On 9 January 2022, Deng moved to
J2 League club
Albirex Niigata. In his first season at the club, he helped them to win the
J2 League title thus gaining promotion to the top tier
J1 League in 2023. On 6 January 2024, Deng's contract was extended for the 2024 season.
Yokohama F. Marinos In January 2025, Deng left Albirex Niigata to join fellow J1 League club, Yokohama F. Marinos. ==International career==