Sharpen left Leonardo, the agency he founded in 2000 for Leo Burnett, in July after it was merged into D'Arcy's Arc agency.
His arrival at Perspectives is a sign that WPP wants to improve the agency's creative standing under the recently arrived chief executive, Miles Murphy.
Perspectives is also moving towards greater collaboration with its sister Red Cell companies, including HHCL/Red Cell.
Sharpen replaces Stuart Burnett, who left Perspectives soon after Murphy's arrival. He started his career at Ogilvy & Mather before moving to Saatchi & Saatchi as the creative director for integration. His creative highlights at Saatchis included work for the Army and Toyota.
After leaving Leonardo, Sharpen considered offers from agencies in the UK and overseas as well as the potential of working on another start-up before taking the Perspectives job.
"We will put highly strategic and creative thinking at the heart of the agency," he said.
Murphy, a former managing director of Grey Desire, said that Sharpen's ability on ambient and digital work, as well as more traditional direct and promotional creative, was a key factor in his appointment.
"We can now work on an equal footing with Red Cell's most creative advertising agencies," Murphy said.
Perspectives was founded in 1987 and has a client list that includes Hewlett-Packard, First Choice Holidays and American Express.