His father Hiddadura Lazarus Mendis was a time keeper at the Ceylon Transport Board and later became an executive officer at Sri Lanka Ports Authority.
[5] His mother Eliadura Karoline Soyza was a teacher at Holy Family Convent, Bambalapitiya as well as practiced music at Haywood.
[10] After finishing education, Mendis along with fellow actor Senaka Perera started to produce a stage play Illeesa.
In November 1979, he acted in another stage play Sathuro produced by doctor Chandrapala, who worked at Ragama rehabilitation hospital.
[5] After appearing in his first teledrama Palingu Menike, Sriyantha entered to the silver screen in 1987, through H. D. Premaratne's movie Mangala Thegga.
Since then, he became a character actor in television where he made several notable characters in the television serials such as Dǣkæthi Muwahatha, Mihikathagē Daruvō, Ingammāruva, Hiru Sandu Hamuvē, Hiruṭa Muvāven, Mæṇik Nadiya Galā Basī, Bōgala Savundiris, Danḍubasnāmānaya, Chala Achala, Bæddegedara, Nǣdǣyō, Akāla Sandhyā, Weda Hāminē, Ves Muhuṇu, Asalvæsiyō, Viśva Bhū Sankrānthiya, Mayarathna and Ruwan Maliga.
Sriyantha has won the Best Actor award for his teledramas Sath Gunalankaraya, Dǣkæthi Muwahatha, Bawa Karma and Viśhva Sankrānthiya.