He replaces Nigel Clarkson, who joined Yahoo as its UK managing director and country commercial director in November.
Pearman will continue to oversee the sales and trading team, and will also be responsible for the propositions and products division.
He joined Weve in 2012 as director of brand and business development, and became sales director in 2014.
Before this, he was head of client sales at Microsoft Advertising having joined the company in 2008 as category development manager.
Robert Franks, the managing director at O2 Commerce, said: "As advertising becomes more and more data-driven it makes complete sense to harness Tom’s expertise and experience in order to lead the growth of our programmatic and insights products and services end-to-end as well as our existing business lines."