The duo, based at GSK's Brentford headquarters, will lead a team of ten split between the US and UK. Mathieson replaces Gwenan Evans, who became director of science comms in March.
Pfizer is seeking to replace Mathieson as soon as possible after she leaves on 7 October. Mathieson, who reports to Pfizer senior marketing manager of customer effectiveness Mark Harrison, conceded the timing of her exit was 'not ideal'.
But she added: 'The procurement team has been involved in the review process for a year, and I am not a one-man band. The decisions on agency selection will be made collectively by the product and procurement teams.'