The duo will jointly lead the 20-strong Isobar Social division, which has grown from around ten staff since it was launched at the end of 2011.
Katie White, the previous head of social, left Glue Isobar in January to join the social media company theAudience.
Glue Isobar opted to split White’s role because it is increasingly providing social media services to brands across markets rather than only in the UK.
James and Caig will report to Penny Herriman, the Glue Isobar chief executive. Isobar Social works on clients including Kellogg and Toyota.