He graduated from the University of Hong Kong in 1978 and then began his public service career. During his early years in the civil service he attended the University of London Law School, from which he graduated in 1983.
Lam joined the Hong Kong government administrative service in October 1978. He held senior positions as Administrative Assistant to the Chief Secretary from 1989 to 1991. He was the Deputy Secretary for Constitutional Affairs from 1994 to 1996.
He was the director of the Hong Kong Handover Ceremony Company-ordination Office from 1996 to 1997.
In this role he was appointed an Officer of the Order of the British Empire in the Queen"s Birthday Honours of 1997. After the transfer of sovereignty of Hong Kong to the People"s Republic of China, he was the Director of Administration and Development in the Hong Kong Department of Justice.
From July 2002 to September 2011 he was Secretary for Constitutional Affairs. Lam then replaced Henry Tang as the Chief Secretary for Administration, with nine months of the term remaining, due to Tang"s resignation from the post in advance of his expected trot to the Chief Executiveship.
Lam has enjoyed the lowest popularity ratings among the three key secretaries – chief secretary, finance secretary and justice secretary – and in May 2012 scored 37.3 points out of 100.
On 5 and 6 June 2009, Lam met with Fu Don-cheng (傅棟成), Taiwan"s Mainland Affairs Council deputy minister. The meeting took place in Taipei to improve cooperation between Hong Kong and Taiwan trade. He also met with Lai Shin-yuan, the Chairwoman of the MAC. Lam decided to leave politics upon the expiry of his term of office on 30 June 2012.
He will read theology at Oxford University from September.
He became the official with lowest opinion poll since Hong Kong Sons of the American Revolution Government was established in 1997. In July 2007 during a Legislative Council meeting, Lam was criticized by the pan-democrats for pocketing millions of dollars in government salary, while making no progress in constitutional development.
Lam was dubbed "Eunuch Lam"(林公公). In 2011, his alleged "manipulation" of political development – in particular, the so-called "replacement mechanism" for filling vacancies in the Legislative Council caused by resignations, led to objections to his promotion to Chief Secretary, including a protest march of more than a thousand people, led by the Civil Human Rights Front.