Tate, who will work closely with the agency’s managing partners, joined Mother as a strategy director in 2007, working across its Coca-Cola brands.
She was promoted to head of brand and new business in 2010. Before joining Mother, Tate was a planner at Bartle Bogle Hegarty.
Andy Medd, a partner at Mother, said: "Sara is a world-class talent who has made a hugely positive contribution in everything she has done at Mother. We could not find a better person in the world to be our first managing director and we are delighted in equal measure for both Sara and for Mother."
News of Tate’s promotion comes shortly after Campaign reported that creative partner Stephen Butler was leaving to join TBWA\Chiat\Day LA, and that Carlos Bayala – founding partner of the agency’s Buenos Aires office – would be moving back to London as a global creative partner.
According to a spokeswoman for Mother, the agency is widening and deepening its management structure to "bring the best people to the fore [and] take advantage of all the opportunities we now have, both locally and globally".