Margaret Batty takes charge of a 15-strong public affairs and policy team.
Batty was formerly deputy director of the European Secretariat in the Cabinet Office. She will work on the charity's End Water Poverty campaign, lobbying at G8 in Japan and the UN. She will also help international advocacy and campaigns teams to lobby in their own countries.
Batty will work with Andrew Cook, director of fundraising and marketing. Head of comms Nick Edmans still looks after the press function.
Batty replaces Stephen Turner, who has retired.
Last year, One PR worked pro-bono with Water Aid to secure corporate sponsorship for fresh2o, a series of celebrity photos used to promote the charity.