Switching causes is not unheard of in the sector, but it still raises a few eyebrows. Mark Goldring, soon to swap international development for learning disabilities, thinks it shouldn't.
"We're selecting my successor now on the basis that he or she could come from any sector," he says. "What matters is that you are a strong, driven leader, not where you have worked before."
Goldring might easily have gone down a different career path: after a short stint as a volunteer teacher in Borneo with VSO when he left university, he trained as a lawyer. But only months into his first job, he found that law wasn't for him.
"I realised I didn't enjoy it as much as working internationally," he says. "So I got into the management side at VSO and worked my way up from there."
He will become the director of Mencap in November, and admits there are significant differences between the two cause areas. But he insists there are shared concerns: "Both are about inclusion. Who benefits, and who is excluded? How do you help people to realise their full potential? There are real links between people who haven't got enough land to live a full life in Bangladesh and people in the UK who can't get a job because no employer will take them seriously. It's about making adjustments to enable them to do it for themselves."
So why change? "My work at VSO was always stimulating, but I increasingly felt that I wanted to do something different," he says. "Because VSO's such a fantastic organisation, there are very few jobs in international development that are as interesting."
Goldring has worked for VSO for a total of 20 years, in three different jobs at different points in his career. At other times, he has worked for Oxfam, the United Nations Development Programme and the Department for International Development.
"If you look at what DfID is trying to do and what agencies such as Oxfam and VSO are trying to do, they complement each other very well," he says. "There is no consensus in the sector on international trade and protection, but on issues such as aid, debt relief and good governance there is a high level of shared understanding.
"The value of those voices in the sector, such as Christian Aid, that disagree on issues such as trade is in warning us of the dangers of unregulated growth and looking at issues of equity and distribution."
One thing Goldring is looking forward to in his role at Mencap is greater involvement in policy and advocacy work. The charity worked hard on the separation of mental illness and learning disability in legislation; more recently it has campaigned to ensure the Disability Discrimination Act considers learning disabilities as much as other disabilities.
Managing the charity's relationship with local authorities will be a new area for him. He says: "Mencap has to play several roles simultaneously - challenging what sort of services are provided and being ready to provide those services itself, sometimes on contract from the same people it's challenging." When asked about his views on the Compact, though, he backs off. "I don't know enough about this yet," he says. "I'm fascinated by it, and it's one of the reasons for moving sectors."
Goldring had to negotiate his notice, asking Mencap's retiring director Dame Jo Williams to stay on a little longer so he could see VSO through a merger with its Canadian counterpart, the CUSO. "So I can't take a break," he says.
2008: Chief executive, Mencap
1999: Chief executive, VSO
1996: Overseas director, VSO
1994: Regional social development adviser for the south Pacific, DfID
1991: Country representative for Bangladesh, Oxfam
1990: Assistant resident representative for Bangladesh, United Nations
1979: Volunteer teacher of English in Sarawak, East Malaysia, for VSO