The Church of England says Hector Sants, a former Barclays executive, will chair the archbishop of Canterbury's task force examining how to support the growth of credit unions.
Sants had been hired by Barclays to help it recover from a series of scandals, but resigned last year after suffering from stress and exhaustion.
Before working at Barclays, he led Britain's main financial regulator during the global banking crisis.
The church post is voluntary and entails work for about a day a month.
Archbishop of Canterbury Justin Welby, a former oil company executive, has been committed to having the church develop plans to help expand credit unions.
The archbishop wants the member-owned financial cooperatives to serve as an alternative to payday lenders, which offer small short-term loans at sky-high rates.