After university, Vitharana worked as a medical officer (1959–67), and was registrar at
Colombo General Hospital in 1963-64. Specialising in
bacteriology and virology, Vitharana joined the Medical Research Institute (MRI) in Colombo in 1972, serving as its director from 1983 to 1994. The
Communist Party of Sri Lanka CPSL and LSSP joined the UPFA in February 2004. Vitharana was appointed a UPFA
National List MP in the
Sri Lankan Parliament following the
2004 parliamentary election. He was appointed Minister of Science and Technology after the election. Vitharana was re-appointed a UPFA National List MP following the
2010 parliamentary election. He lost his cabinet position after the election but shortly afterwards, in May 2010, he was appointed
Minister of Technology and Research. He was promoted to Senior Minister of Scientific Affairs in November 2010. He lost his cabinet position following the
2015 presidential election. At the
2015 parliamentary election, Vitharana was placed on the UPFA's list of National List candidates. However, after the election he was not appointed to the National List. Vitharana was awarded the
Vidya Jyothi title in
2017. On 4 December 2019, Vitharana was appointed Governor of the
North Central Province, Sri Lanka. He was sworn in before President
Gotabaya Rajapaksa. ==Personal life and death==