Greenwood has been on the firm's board for 10 years and has also held the role of board chair.
She said the past 18 years had exceeded her expectations.
"Russell McVeagh is a great firm and has wonderful people in it, and I have been fortunate to work with some of the best in our industry.
"I leave the firm in great hands and I look forward to watching Jo Avenell lead the firm into a new era of success."
She leaves the firm in March 2019 and plans to expand her directorship roles at Fisher & Paykel Healthcare and Spark, as well as taking on other governance positions.
Board chair Malcolm Crotty said Greenwood was a credit to the organisation.
"In addition to her professional excellence, Pip has played a leading role in changes within our profession. I am grateful to Pip for putting her own plans on hold in order to lead the internal changes as interim CEO and she leaves the firm well placed to continue with a revitalised culture."