Ms Reynolds will start her new position at UNPRI's London-based office in February and AIST aim to appoint her successor before the close of the year.
As managing director of UNPRI, Ms Reynolds will focus on boosting signatory relations and outreach through promoting the benefits of the principles for responsible investing (PRI).
"There is a strong match between the objectives of long-term, institutional investors and the aims of the PRI," Ms Reynolds said.
"I firmly believe that global investors working together can achieve the PRI's goals of a sustainable financial system that makes an active contribution to improve global governance and ESG engagement."
The news comes just weeks after AIST announced government funding for The Super Springboard Program, which aims to improve the gender gap on superannuation boardrooms.
The program saw the federal government provide $150,000 towards the 12 month mentoring program, to give 10 scholarship recipients training in the industry.
"With Fiona at the helm, AIST had led the way in governance and disclosure reforms and been a key driver in improving retirement outcomes for low income earners and women," AIST president Cate Wood said.
