The merged operation will be led by former Shire Health London MD Matt de Gruchy.
Shire Health International MD Antonia Betts will report to de Gruchy, taking the title director of operations and European development (PR).
The aim of the merger is to ‘give clients greater access to senior talent and allow staff expertise to be deployed across both agencies, rather than one,' said de Gruchy.
He added: ‘Longer term this will help us to roll out additional service offerings.'
De Gruchy has worked for both SHI and SHL for around ten years, spending the past three as MD of SHL. Betts also has around ten years' experience with the group, following seven years as MD of SHI.
De Gruchy said all 20 SHL and 35 SHI staff would be retained, adding that the agencies' six senior managers would work under de Gruchy and Betts as ‘business unit leaders'.
The two agencies are already based in the same London office.
De Gruchy reports to Ogilvy Healthworld group MD for the UK, Emma Sergeant, who replaced Gloria Gibbons in May.
Gibbons is now Ogilvy Healthworld president for Europe, taking over from Conservative Party vice-chair Margot James, now a part-time consultant.