Sarah Nelson will take up the role in mid-January, filling the post left vacant by Martin Broughton's departure to Reuters' humanitarian-themed news website AlertNet. Nelson, who has been at Samaritans for five years, said she had always wanted to work for an international charity.
Broughton left last week after seven years at MSF. Content officer Lucy Clayton is the role on an interim basis until January.
Nelson will take charge of a six-strong team and report to UK chief executive Jean-Michel Piedagnel.
MSF's humanitarian work spans 70 countries, including some of the poorest in the world. Its founder - the former French health minister Bernard Kouchner - failed in his bid to become the new head of the World Health Organisation this Monday.
Plans for Nelson's replacement at Samaritans are yet to be decided.
ALSO... Samaritans launched its traditional winter campaign this week, targeting vulnerable young men.
It is releasing research by The Dream Mill Consultancy listing the top ten worries for young people - such as debt and exams.