Trish Donohue will leave Cbus in December after 17 years with the fund, including 13 in an executive role.
A Morningstar analyst note on the departure said Ms Donohue was one of the founding members of the Cbus investment team "and has been a key influence in the growth of the fund since 2004".
However, the research house said Ms Donohue has not been involved in day-to-day investment management of the fund in her current role and there will be "minimal effects" on the day-to-day management of the assets of the fund as a result of her departure.
A Cbus statement said Ms Donohue is leaving the fund "to explore further career opportunities", and that the structure of the investment team will be reviewed by chief executive David Atkin and chief investment officer Kristian Fok in the "coming months".
