Sadasivan joined Tan Tock Seng Hospital as a consultant neurosurgeon in 1991, where he reorganised the way stroke patients were treated, arranged for the neurosurgical intensive care unit to be computerised, introduced stereotactic brachytherapy for dealing with brain tumours, and chaired the National Neuroscience Institute's planning committee.
Ang Mo Kio GRC was contested by the Workers' Party of Singapore in the general election of 2006, and Sadasivan retained his seat, the PAP winning with 66.14% of the votes polled in the constituency [REF].