Farrell joined Rio in 1987 and over the years held various roles across human resources, health, safety, communities and environment.
She joined the executive committee in July 2016 when she took on her current role and that of managing director for Australia.
Before joining Rio, she worked at BHP and prior to that was an economist in regional development with the Government of Western Australia.
Rio CEO Jean-Sebastien Jacques thanked Farrell for her leadership and support, and for the significant impact she has had across the company and the industry as a whole.
The company plans to announce what will happen the health, safety and environment leadership role before she departs in September.