In 2000, contested the General Election as a candidate from the Sri Lanka Freedom Party in the People's Alliance.

He became the youngest person to be elected to parliament at the age of 21 polling the highest majority of votes from the Anuradhapura district.

In the General Election of 2004 he retained his seat in parliament and was appointed Deputy Minister of Skills Development, Vocational Training and Technical Education Ministry a post he held till 2005.

At the start of his first term, President Mahinda Rajapaksa appointed Dissanayake as the Deputy Minister of Port and Aviation in 2007.

During this time, the Ministry started to explore for oil around Sri Lankan sea and decided to excavate the Mannar basin.