He joined Shire Health International around eight months ago after an initial two-and-a-half-year stint with Galliard, latterly in an account manager role.
Elliston said: 'The opportunity to rejoin was just too good to pass up.'
Galliard has also hired Saoyuth Nidh, a French national, to a senior account manager role. She is working on the company's Roche anaemia business.
She has formerly worked for Manning Selvage & Lee in London and for Burson-Marsteller at the agency's offices in Paris.