Mah began his career at the Singapore Bus Service (SBS) from 1973 to 1983, rising to become its general manager. He was then seconded to Singapore News and Publications Ltd (SNPL) as the Chief Executive Officer of the Singapore Monitor newspaper. From 1985 to 1988, he served as the Group General Manager of SNPL and Group General Manager (Co-ordination) of Singapore Press Holdings Ltd.
Mah entered politics at the 1984 general election, when he stood unsuccessfully in the constituency of Potong Pasir, where he was defeated by Chiam See Tong of the opposition Singapore Democratic Party. Prime Minister Lee Kuan Yew was thought to have played a role in Mah's defeat, having been seen as being unnecessarily dismissive in comparing Chiam's average GCE Ordinary Level results to Mah's stellar academic achievements.
In 1988, Mah was elected as a Member of Parliament (MP) for Tampines GRC, winning 61% of the vote. He was re-elected as an MP for Tampines GRC at the 1991 general election with 59.48% of the vote, and by walkover at the 1997 general election. At the 2001 general election, he was re-elected with 73.34% of the vote over the slate from the Singapore Democratic Alliance (SDA). At the 2006 general election, he was re-elected with 68.51% of the votes over the SDA. At the 2011 general election, he was re-elected with 57.22% of the votes against the National Solidarity Party.
In 1990, Mah was appointed a Minister of State at the Ministry of Trade and Industry and Ministry of Communications by Prime Minister Goh Chok Tong. He was appointed Acting Minister for Communications in 1991, concurrently holding the post of Minister of State for Trade and Industry.
Mah served as Singapore's Minister for Communications from 1991-99. He concurrently served as the Minister for the Environment from 1993-95. He was appointed Minister for National Development in 1999 and served until 2011. He also served as Deputy Leader of the House in the Parliament of Singapore from 2002-07, and as Leader of the House from 2007-11. He retired from Cabinet in 2011 after the general elections and retired from politics in 2015 without contesting the 2015 general election.
Mah has also held several other public service positions, including Chairman of the Board of Directors NTUC Comfort from 1983–86; Chairman of the National Productivity Board, National Productivity Council and Skills Redevelopment Fund Advisory Council; Chairman of the Board of Governors of the Singapore Institute of Labour Studies from 1990–2002; and President of the Football Association of Singapore from 1999-2004.
After stepping down from the government cabinet, Mah Bow Tan was appointed as an independent director and non-executive chairman at Global Yellow Pages in September 2011.
Mah was educated at St. Michael's School (now known as St. Joseph's Institution Junior) and St. Joseph's Institution. He then received the President's Scholarship and Colombo Plan Scholarship to study at the University of New South Wales (UNSW) in Australia, where he graduated in 1971 with first class honours in industrial engineering, winning the University Medal (the prize for the top student in each department). He also completed a Master of Engineering in Operations Research at UNSW in 1973. (He was awarded an honorary doctorate by UNSW in 2001.)
Mah is married to Sheryn Kaye Von Senden. The couple has two sons and two daughters.
Mah is a passionate soccer fan. He also enjoys travelling, photography and golf.
The Flower Dome and Heritage Garden have named the dendrobium Mah Bow Tan in his honour.