The fourth annual leaders' retreat is a "key bilateral platform for both Prime Ministers to drive relations forward", the Ministry of Foreign Affairs said in a statement today.
PM Lee and Mrs Lee will host a private dinner for Mr Najib and his wife Rosmah Mansor tonight.
The two Prime Ministers and their ministerial delegations, will meet on Tuesday morning for bilateral discussions.
Both Prime Minister will then make site visits to several joint ventures by Temasek Holdings and Khazanah Nasional in Singapore and in Iskandar Malaysia.
In Singapore, they will unveil the Marina One project in Marina Bay and receive an update on the DUO project in Ophir-Rochor, which are both mixed use developments.
They will then travel to Iskandar Malaysia to unveil the Urban Wellness and Resort Wellness projects in Medini, and do a ground-breaking for the Urban Wellness project.