DAMMAM, Saudi Arabia—Saudi Arabia’s sovereign-wealth fund said Monday that it will acquire a 50% stake in an investment company led by Emirati businessman Mohamed Alabbar.

The deal comes after Adeptio AD Investments SPC Ltd. last month completed the purchase of a majority stake in Kuwait’s Americana, one of the Middle East’s largest operators of fast-food chains including KFC, TGI Friday’s Inc. and Pizza Hut.

The Public Investment Fund said the transaction is part of a plan to “increase investment in non-oil sectors and build a portfolio that has greater geographical and asset class diversification.”

The Saudi wealth fund stands at the center of the oil exporter’s economic reform plans as it works to reduce its dependence on the commodity.

The fund didn’t disclose the deal’s financial details but said Mr. Alabbar will retain a 50% stake in Adeptio.

Mr. Alabbar and the PIF earlier this month announced launching an e-commerce company at an initial investment of $1 billion. The new venture that will begin operations in January, called “Noon,” will offer 20 million products—ranging from fashion to electronics—to Middle Eastern households, the investors said.

The latest deal is the fourth major investment announced by PIF this year.

The fund in June said that it has invested $3.5 billion in Uber Technologies Inc. before announcing last month that it is teaming up with Japanese internet and telecommunications giant SoftBank Group Corp. to create a multibillion-dollar technology-investment fund.

The PIF manages around 200 investments, including shares in 20 companies listed in the Saudi stock market, in addition to its investments abroad. The total value of assets currently managed by the PIF is around 600 billion Saudi riyals ($160 billion), the fund said.

Mr. Alabbar is best known for leading real estate giant Emaar Properties, which built the Burj Khalifa in Dubai. But he has also become increasingly active as an investor, striking deals across several sectors.

Earlier Monday, Mr. Alabbar and Italian web-based luxury fashion retailer Yoox Net-a-Porter announced a €130 million joint venture to tap the fast-growing online market in the Middle East. Mr. Alabbar is also leading up a $1 billion regional technology fund that he said Monday would make its first investment in the next couple of months.

Write to Ahmed Al Omran at Ahmed.AlOmran@wsj.com