In 1969, Tan served as the general secretary of the university students' union. In 1972, he began assisting in Kuo Chuan constituency, where he learned about the needs of the working-class of Singapore society. It is his strong desire for social equality and improving the lives of the less fortunate that has made his parliamentary speeches well known amongst his fellow MPs. Tan took a 13-year break from speech-making when he became speaker. He is remembered for his fairness to both sides of the floor of the house, allowing members of both the ruling party and the opposition to speak their minds. He is also remembered for his sense of humor, for his notes to fellow MPs would be signed off "The Watchman", a take on his private business, and his role as speaker. During his stint as the speaker, he was also president of the AIPO for the 1989–1990, 1994–1995 and 1999–2000 sessions. He also twice served ex officio as acting president when the President of the Republic and deputy prime minister were both out of the country on official business. Tan also supervised the building of the new Parliament House, heading the Committee on the Parliament Complex Development Project. The new building was completed in 1999, and a ceremony was conducted to officiate the "move" from the old Parliament House near the Supreme Court to the new one along the Singapore River. Currently, he is the private principal secretary to former transport minister Lui Tuck Yew.
Backbenching
In April 2002, when he stepped down as speaker after 13 years, Tan immediately made it known that as a backbencher, with his brutal honesty and openness, he could still "shake the House". Many of his speeches provided witty, pointed, even scathing, remarks about certain government policies and expenditures, such as the extravagance of certain public buildings and the rising cost of public transportation. He apologised in the same year over a speech for deliberating misleading Parliament and Singaporeans. In a tribute by Prime Minister Lee Hsien Loong on April 15, 2006, he said of Tan, "He makes very good speeches in Parliament. Sometimes, he draws blood... Sometimes he has offended ministers, but he has spoken his mind." Having retired from politics, he aims to devote more of his time to his business, his family and friends. Most of all, he will be spending more time with his band, a group of schoolmates from ACS and university, known as The Young Once, which has been a regular appearance on charity events, since they formed in the late 1990s, while Tan was still Speaker of Parliament.