He has a background in the commercial sector where he was group director of strategy for the Lattice Group, a gas and electricity delivery company.
Previously he was a director of Transco and worked for BP for 24 years.
Ainger succeeds Michael Brophy who has retired after 20 years leading the organisation.
Sir Brian Jenkins, CAF's Chairman of Trustees, said: "In Stephen Ainger, we have found the best person to succeed Michael Brophy.
"He has all the right instincts and experience to take CAF forward and to meet the challenges posed by the need to generate greater charitable resources."
"This is an enormously exciting opportunity for me," said Stephen Ainger.
"Charitable activity is something very close to my heart and in which we all have a role to play."