Manwani - the first ever COO of Unilever - will however, continue as Non-Executive Chairman of Hindustan Unilever Ltd, the Indian arm of the Anglo Dutch firm, a statement said.
Unilever CEO Paul Polman said: "Harish is an inspirational leader and leaves a remarkable legacy. He has been at my side in helping to drive the turnaround of Unilever, making this once again one of the most admired companies in the world".
He added that under Manwani's leadership Unilever saw a step-change in "its go-to-market organisation and there has been a relentless focus on flawless execution globally".
"He has role-modelled the 4G sustainable growth model - competitive, consistent, profitable and responsible - which has become such a strong focal point for the markets," Polman added.
On his imminent retirement, Manwani said: "I am deeply grateful to all those colleagues, who have helped to make the last 38 years at HUL and Unilever so memorable and fulfilling. It has been a privilege to serve such a great company...I look forward to working with Paul and the leadership team over the coming months to ensure a smooth transition and to further build our growth agenda."
As Chief Operating Officer of Unilever, Manwani has been credited for establishing and aligning market clusters across the world behind a clear agenda, creating a better and more integrated go-to-market organisation.
"It has also allowed the business to be managed more dynamically, resource allocation to be done more efficiently across markets and best practices to be transferred more seamlessly. This has allowed Unilever to become increasingly more competitive in a tougher business environment," the company's statement added.
Manwani had joined HUL in 1976 as a Management Trainee and was elevated on HUL Board in 1995 as a Director responsible for the Personal Products business.
In 2005, he was elevated to a greater role in Unilever's structure and was appointed as Executive for President, Asia, Africa, Middle East. The role later expanded to include Central and Eastern Europe.
Manwani also became the first Non-Executive Chairman of HUL and has overseen a period of sustained growth with the business more than doubling its size and reinforcing itself as one of India's most admired companies.
He is a member of the Board of Directors of Whirlpool Corporation, Pearson and Qualcomm Incorporated. Apart from that Manwani also serves on the Board of the Indian School of Business and the Economic Development Board (EDB) of Singapore.