Harper will join on 4 July as number two to the agency's MD of London healthcare practice and European healthcare chief Fiona Hall. She will be deputy MD of UK healthcare, a newly created role.
She has spent seven years at SHL in two different spells, rejoining the agency in 2001 after a two-year stint at Burson-Marsteller.
Hall herself joined WS from SHL, where she was managing director (PRWeek, 27 November 2003).
Hall said she would be 'enabled to focus more on growing (WS business in) Europe' when Harper arrived.
Harper's looming switch follows the news that WS healthcare director Roy Stairmand, who has formerly worked at Hill & Knowlton and Ketchum, left in April after three years with the agency.
At WS, Harper will lead the agency's global account for Pfizer/Sanofi-Aventis's inhaled insulin Exubera (aside from US work, which will continue to be led by WS in the US). She will also lead its work on a recently won but currently undisclosed global account.
Other directors in WS's UK healthcare arm include Sally Evans, Antoinette Dale-Henderson and Neil McGregor-Paterson, the former UK health and medical division MD at Ogilvy PR Worldwide who joined at the end of last year.
Recent hires include former SHL account manager Helen Limbrick, who has joined in the same role after a short spell at Munro & Forster Communications earlier this year.
WS London now has around 23 staff working on healthcare accounts. Hall said the agency was recruiting 'at all levels'.