[1][2] Lionel started his career with National Football Academy (NFA) U-18 team in 2015 after his graduation from the Singapore Sports School.

However, when no such move arose, Tan jumped at the chance to be reunited with Robin Chitrakar at Home United's Prime League squad.

[1] He made his debut for the Cheetahs against Tampines Rovers, coming on as a substitute in the 61st minute before earning a shock first start in the following match against Brunei DPMM in a 2–0 defeat.

[5] Lionel returned to Hougang United after the completion of his National Service in the middle of the 2020 Singapore Premier League season.

[5] He scored the first professional goal of his career in the third match of the 2021 Singapore Premier League season, sweeping in a loose ball and helping his team to a shock 3–1 win against powerhouse Lion City Sailors.

In 2017, Lionel was called up to the Singapore Under-22 squad for the 2017 Southeast Asian Games but failed to make a single appearance as the Republic crashed out in the group stages.