Purnell, who was a minister in both Tony Blair and Gordon Brown's administrations, will also keep responsibility for his current role as head of radio and education, which he took on in September.
Earlier this month the BBC announced the departure of Aaqil Ahmed, who was the BBC’s first Muslim head of religion and ethics.
In the past the corporation has polarised opinion on it from different faiths, with some asserting that the BBC’s coverage of religion and religious affairs is biased towards Christian faiths - an accusation strongly dismissed by some Christian leaders who claim there is not enough.
The BBC attests that it aims to increase its coverage of other faiths, while maintaining the same level of output for its Christian coverage.
A BBC spokesman quoted anonymously by the Christian Today website said that Purnell’s role will not be as head of religious affairs but more as a representative of religion at the top table of the corporation.
It is understood that Lord Hall of Birkenhead - the director-general of the BBC - will sit down with UK religious leaders in January to discuss the role of religion in British society and how the BBC can accurately reflect that.