Formerly head of research and market intelligence at Bespoke Communications, Tagg will now work in Synovate's financial and business services sector team.
With over 12 years of financial services experience, his new role will include account management and business development along with further extending Synovate's reputation and presence in the sector.
Tony Smith, head of the financial and business services team, said: "We're delighted that Stuart is joining us.
"Financial services is a growing sector for Synovate and we're continually looking for talent around the globe.
"Stuart's focus on financial markets and experience gained over the last 12 years further strengthens our capabilities in this key area."