This three-day portion of the conference brings government leaders, ministers and heads of international agencies together, and is where agreements are expected to be finalised.
Mr Lee, whose attendance here is a demonstration of Singapore's commitment to tackle climate change, will address the conference this morning, said a statement from the Foreign Affairs Ministry.
The conference on the Indonesian resort island of Bali aims to get negotiations going on a new international climate change agreement to replace the existing Kyoto Protocol, which will expire in 2012.
During his time here, Mr Lee will also have bilateral meetings with three leaders: Indonesian President Susilo Bambang Yudhoyono, newly elected Australian Prime Minister Kevin Rudd and Papua New Guinea Prime Minister Michael Somare.
Mr Lee will also attend a leaders' retreat hosted by Dr Yudhoyono tomorrow.
Accompanying Mr Lee on the trip are Environment and Water Resources Minister Yaacob Ibrahim and other senior officials.