Barrell has held various senior comms roles at Shelter since joining in 2000, and has also worked as a cameraman and journalist for news agency Reuters.
Weir said he was chosen because of his mix of 'strategic thinking and creative comms ideas'. She added: 'We were looking for a fresh approach, and felt Joe could give us a more gutsy, edgy feel to our communications.'
One of Barrell's tasks will be to build awareness of the charity's work in the UK. High-profile activity abroad has long established Save the Children as a global charity, but it is keen to draw attention to its work tackling UK child poverty.
His role also covers internal comms, and he will be expected to help regional teams around the world become more self-sufficient.
Because his arrival coincides with that of chief executive Jasmine Whitbread, one of his first tasks is likely to be communicating strategies introduced by the ex-Oxfam international director.
Barrell said he had worked extensively on social justice for children while at Shelter, and was looking forward to the challenge of working with Save the Children.
'The Make Poverty History campaign has changed the landscape for charities, and I am very excited about joining Save the Children during a major period of change,' he said.