Pitkethly, who has been with the maker of Dove soap since 2002, succeeded Jean-Marc Huët as finance chief in 2015.
The 56-year-old previously served as executive vice president of Unilever's UK and Ireland business, including head of M&A and head of treasury.
The announcement of his departure comes as Unilever, like the rest of the consumer goods industry, is grappling with significant cost inflation and pressure on its margins due to high prices for energy and other commodities.
Unilever, which did not say why Pitkethly planned to "retire from the company", said it would proceed with a formal internal and external search for his successor.
One of the biggest consumer companies in the world with more than 400 brands ranging from detergent to ice cream, Unilever in January appointed Hein Schumacher to replace CEO Alan Jope from July.
That move was welcomed by investors including board member and activist shareholder Nelson Peltz.
"The timing of Pitkethly's retirement announcement is maybe not a surprise, as this will give the incoming CEO the opportunity to reshape his leadership team," said Tineke Frikkee, a fund manager at Unilever shareholder Waverton Investment Management.
"Eight years as CFO of a multinational is a decent time and retiring in May 2024 should enable a useful handover to a new CFO."
The company also said Conny Braams, its chief digital and commercial officer, had decided to leave Unilever in August
(Reporting by Eva Mathews in Bengaluru and Richa Naidu in London; editing by Shailesh Kuber and Jason Neely)
By Richa Naidu and Eva Mathews
