The service, to launch this month, will let fundraisers accept international donations and reclaim tax from UK taxpayers through the social networking website.
Facebook users can personalise their profile pages to show they are fundraisers. The members of their contact networks can give to charity by clicking through to Justgiving. Trails of which contacts are speaking to whom about supporting causes will also be visible.
"It's a perfect fit for Facebook users who are doing a sponsored event or have created their own appeal," said Matthew Knight, technical architect at Justgiving. "You would be hard pushed to find an easier way to engage friends and contacts."
An estimated 10-15 per cent of Justgiving users have Facebook accounts.