Kalifa departs after two years with the company.
Rebrand will officially launch in March 2025 as the agency celebrates its 30th anniversary.
Holding company did not previously have entire ownership of The & Partnership, which merged with MSix & Partners to form T&Pm.
Account was won following a competitive pitch.
Ahmed founded the business in 1994. It was acquired by WPP in 2012.
Brett Marchand will be interim group chief executive.
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