The partnership deal - which will be completed by 1 January - will see Shire Health, one of the UK's largest healthcare PR and medical education firms, become part of O&M's healthcare advertising, direct marketing and PR businesses, with a view to working on clients in tandem.
O&M's PR arm - Ogilvy PR Worldwide - has an established healthcare practice, but acknowledges it is stronger in the US and Asia than in Europe.
Ogilvy PR global CEO Marcia Silverman said this deal would give Ogilvy 'strength and leadership' in the European healthcare communications market.
Shire Health chairman Margot James said the coming to market of more products with a 'strong consumer dimension' had played a 'significant' role in the Ogilvy link-up.
'The environment is getting more liberal although I don't see any legislative change that will revolutionise the market for the next three to five years.
This enables us to draw on Ogilvy's strong consumer brand,' she added.
Shire Health CEO Gloria Gibbons said Ogilvy clients would benefit from its pre-marketing divisions, which work in fields 'earlier in the product development process' such as clinical trial recruitment and pre-launch medical education.