Gan made his political debut in the 2001 general election as part of a five-member PAP team contesting in Holland–Bukit Panjang GRC and won by an uncontested walkover.

Gan was educated at Catholic High School and National Junior College before he received an Overseas Merit Scholarship from the Singapore Government to study at the University of Cambridge, where he completed a Bachelor of Arts degree in electrical engineering in 1981.

Gan made his political debut in the 2001 general election as part of a five-member PAP team contesting in Holland–Bukit Panjang GRC and won by an uncontested walkover.

During the 2006 general election, Gan replaced Low Seow Chay as the PAP candidate contesting in Chua Chu Kang SMC and won 60.37% of the vote.

During the 2011 general election, Gan led the five-member PAP team contesting in the newly-formed Chua Chu Kang GRC and won 61.20% of the vote.

During the 2015 general election, Gan led the four-member PAP team contesting in Chua Chu Kang GRC and won 76.89% of the vote.

During the COVID-19 pandemic in Singapore, Gan and Lawrence Wong were appointed co-chairs of a multi-ministerial committee set up by the government on 22 January 2020 to manage the situation.