He is the founder, chairman and CEO of WSO2, [2][3] an open-source middleware company, and creator of the Ballerina programming language.

He has been instrumental in positioning Sri Lanka as a global technology center:[4] In addition to founding WSO2, he started the Lanka Software Foundation to provide a platform for Sri Lankan software engineers to contribute to global open source initiatives.

A staunch supporter of education and transparency, he is the founder of the Avinya Foundation, a non-profit dedicated to assisting underprivileged students.

After graduation, Weerawarana joined IBM Research working in Hawthorne, New York, until he left to found the startup WSO2.

[5] Weerawarana set up the Lanka Software Foundation, and was involved with the Sahana FOSS Disaster Management System.