McCallum-Deighton left Lowe Fusion almost a year ago (PRWeek, 19 November 2004), moving to medical comms agency Mudskipper Bioscience in a board-level position.
Prior to Lowe Fusion, where he worked for around 18 months,
McCallum-Deighton was managing director of Healthcare Education Services.
Edelman London CEO Stuart Smith said McCallum-Deighton would provide senior counsel to existing clients while also helping to bring in new business.
BioScience achieved double-digit growth last year and McCallum-Deighton has been briefed to help sustain the 16-strong division's upward trend, said Smith.
He joins Edelman less than a month after the agency unveiled the appointment of former Hill & Knowlton UK healthcare boss Mike Kan as its new managing director of UK healthcare (PRWeek, 2 September).
McCallum-Deighton reports to Kate Triggs, the agency's executive vice-president and managing director of healthcare Europe.
Accounts he will work on include The Future Forum, an initiative sponsored by an educational grant from drugs firm AstraZeneca that debates the need for improved standards in vascular disease management.
Edelman clients also include Pfizer and Johnson & Johnson. Other senior figures in its BioScience business include associate director Laura McKeever.