Sheikh Ahmed bin Saeed al-Maktoum, who is also the uncle of Sheikh Mohammed, will replace Abdulla al-Habbai in both jobs, the tweet said, without giving further details.
Dubai Holding manages 130 billion dirhams (£27 billion) in assets, employing 20,000 staff across ten countries, according to its website. Dubai-based Meraas is also linked to the ruler and his family.
The appointment is part of a new expansion strategy at both companies, while also consolidating their brand profile, reported state news agency WAM.
Dubai Holding, whose operations will continue as normal, and Meraas will remain separate, independent companies, Dubai Holding said in a statement.
"I look forward to driving the Group’s strategic vision. With the support of the capable teams across the businesses, I am confident that we will continue to build on our track record and contribute to Dubai’s diversification strategy," Sheikh Ahmed said in the Dubai Holding statement.
Meraas did not immediately respond to requests for comment.
Dubai, a regional business hub and a shopping destination for Middle Eastern and South Asian travellers, has seen its retail and property sector suffer in recent years due to an economic slowdown in the region.
In September, Meraas and Canada's Brookfield Asset Management agreed to form a joint venture valued at 5 billion dirham (£1.1 billion) to own and operate Meraas' retail assets.
Sheikh Ahmed oversees a number of state entities including airline Emirates and bank Emirates NBD. He is also a Dubai government official.
(Reporting by Nafisa Eltahir, Additional reporting by Alexander Cornwell; Writing by Saeed Azhar; Editing by Dale Hudson and Mark Potter)
