Hillman will join as global director of external relations - a newly created role based in Seattle.
Hillman said that promoting overseas aid in the current climate was a 'huge challenge'. His comments came after PRWeek reported last week that charities such as ActionAid and Cafod are stepping up their PR efforts in the wake of negative media coverage.
Hillman said: 'The foundation is trying to raise its profile on issues such as global development and health in Europe and the G20 countries. It is very keen on exploiting ways to be more involved in the digital space.'
Hillman added that his priority would be to make sure that the foundation is 'telling a consistent global story working across a huge number of countries'.
He emphasised that social media will play a large part in the comms operation, allowing the organisation to speak directly to the public.
'Social media is one of those massive growing areas - think of the incredible reach of Facebook, new platforms and the proliferation of mobile in Africa. Some of my focus will be on how we can create content across diverse platforms.'
The Gates Foundation was set up by Bill and Melinda Gates in an attempt to improve healthcare and reduce extreme poverty globally, while also expanding educational opportunities and access to IT in the US.