[1] Premajayantha received his primary and secondary education at St. John's College, Nugegoda.

[4] Premajayantha began his political career in 1991 being elected as the Deputy Chairman of Sri Jayewardenepura Kotte Urban Council.

With the formation of the United People's Freedom Alliance in 2004, Premajayantha was made its inaugural General Secretary of the party.

Few days prior to the elections he was removed from the position by the party Chairman, President Maithripala Sirisena.

[9] After the Sri Lanka Freedom Party and United National Party signed a Memorandum of Understanding to form a National unity government,[10] Premajayantha became the Minister of Technology and Research[11][12][13] He was reappointed as the Minister of Education on 20 May 2022 by President Gotabaya Rajapaksa and again by President Ranil Wickramasinghe on 23 July 2022.