Hired in 2015, partly to help restore sluggish sales in its Eastern Europe division, including Russia, 't Hart has successfully overseen Carlsberg's SAIL'22 strategy, which focused on cutting costs and improve sales of more premium beer brands.
'Given his strong track record and the lack of a clear successor, we see today's news as negative,' JP Morgan analysts said in a note.
Carlsberg said in a statement that 't Hart planned to leave by the end of the third quarter. Shares in the brewer were down 2.5% at 8:25 GMT.
"Cees 't Hart has delivered remarkable results during his time at Carlsberg," supervisory board chair Henrik Poulsen said.
Third Top Brass Exit
"It's sooner than I expected," Jyske Markets analyst Henrik Hallengreen Laustsen told Reuters.
"He has really been a significant person in the transformation that has taken place, it's been very impressive to witness," Laustsen added.
Carlsberg, the Western brewer most exposed to Russia, said last year it expected a writedown of about DKK 9.9 billion (€1.33 billion) after announcing a sale of its business in the country as a result of Moscow's invasion of Ukraine.
"Staying on board for another half a year will allow me and the team to continue delivering on our challenging plans for 2023 and accomplishing the sale of the Russian business before the summer," 't Hart said.
Carlsberg said it expects to have found a buyer and signed an agreement by June. It is seeking an option with the buyer to buy back the Russian business in future.