De Koning attended Padua College[2] and played junior football for Mt Martha with current teammate Jacob Weitering[3] and St Kilda player Hunter Clark. He typically played as a ruckman.[4] De Koning joined TAC Cup club Dandenong Stingrays and kicked nine goals in 2016 as a 17-year-old against the Northern Knights.[5] He joined the AFL Academy, played 11 TAC Cup games and kicked 17 goals.[2] De Koning lacerated his kidney in July 2017 after a fall in a ruck contest, but recovered and was drafted by Carlton with pick 30 in the 2017 AFL national draft.[3] In 2018, De Koning extended his contract until 2021,[6] and made his AFL debut in round 22 against the Western Bulldogs at Docklands Stadium. He recorded 11 disposals, five marks and kicked his first goal in the second quarter.[7] Tom extended his contract with the Carlton Football club until 2025.