[1][3][4][5] Clark was born in London and educated at Charterhouse School and Merton College, Oxford where he studied Mathematics and Philosophy.

He owns a company called Thai Open Source Software Center, which provides him a legal framework for his open-source activities.

Clark served as technical lead of the working group that developed XML—notably contributing the self-closing, empty element tag syntax, and the name XML.

[citation needed] Clark is the author or co-author of a number of influential specifications and implementations, including: Clark is listed as a member of the working group that developed the Java Stream processing API for XML (StAX) JSR 173 at the JCP.

This work included pushing the Thai localization of OpenOffice.org office suite and the Mozilla Firefox web browser, along with other open source software packages.