Tom Wright, the chief executive of Age UK, has become chairman and non-executive director of a marketing company for older people.
Rhc advantage was founded by a marketing consultant, Mark Beasley, to provide marketing and communications services for clients seeking to "develop greater competitive advantage" with older people in the UK.
A spokeswoman for the charity said Wright devoted "a few hours each month" to the unpaid role and it had "no impact on his time commitment to Age UK".
She added: "This was agreed fully by the chairman and remuneration committee of Age UK, who would approve only those new opportunities that they believe to be complementary to the work of Age UK."
A senior figure at one local Age Concern, who did not wish to be named, questioned the move. "Charities are expected to be ethical organisations, while commercial entities make profits," he said. "The two do not necessarily coincide."
The Acevo Pay Survey 2010/11 revealed that 3.5 per cent of charity chief executives sit on the boards of private sector companies.