The agency will collaborate with the organisation’s team, partners and supporters to raise awareness of Save the Children’s cause and work around the world.
There is no incumbent on this account but Save the Children will continue to work with existing agencies Adam & Eve/DDB in the UK and J Walter Thompson internationally.
Save the Children International, which launched in 1919 and now serves millions of children, is gearing up to make its centenary a major moment across the world.
The organisation's chief executive is Helle Thorning-Schmidt, the former prime minister of Denmark from 2011 to 2015.
Thorning-Schmidt said: "We will use our centenary to help accelerate progress towards a safer world for every last child."
"We know we can do better, and with Mother’s help, 2019 will see us redouble our efforts to reach more people with our urgent message of hope, action and belief."
Mother founder and chairman Robert Saville added: "Our hope is that we can help mobilise a vast army of people around the world to help make this centenary a single, powerful call to action on behalf of Save the Children, uniting anyone who truly cares to make sure the next one hundred years have to be safer for children everywhere than the last."