Macnamara’s new role marks a return to the digital media company, where he spent five years as an agency sales manager until 2005.
Macnamara will be responsible for seeking out growth opportunities and new revenues. He will report to Georgia Giannattasio, AOL’s head of multinational.
After leaving AOL in 2005 Macnamara worked at RealNetworks and Yahoo before joining Tremor Video as its commercial director. He was promoted to UK managing director in 2013.
Macnamara said: "Returning to AOL after a ten-year absence is a hugely exciting prospect for me.
"AOL is a pioneer in the digital ad space and continues to evolve and break down industry barriers. It's a fantastic time to be joining the business, there are endless opportunities for advertisers and there's an incredibly dynamic team already in place."
His appointment follows a number of senior hires to AOL’s multinational sales team, including international sales directors Clare Pederson from The Guardian and Thomas Bailly from Microsoft.