Brian Tjugum leaves to join One as its European campaigns director on 1 August.
Tjugum said: ‘It was a difficult decision to leave Weber Shandwick but after nearly six years with the agency, I feel the time is right for a change.
‘I’m excited about the potential at One and thrilled that I’m joining at a time when the organisation is beginning a new phase with new leadership, new energy, and renewed commitment to social change.’
The news follows the appointment of Adrian Lovett, who also joins One in August to take the role of Europe executive director. He leaves Save The Children after four years’ service.
One raises awareness about the crisis of extreme poverty and presses governments to support policies aimed at saving lives.