MGM Resorts International said a joint venture that includes Blackstone Group Inc. would buy the real estate of the MGM Grand and Mandalay Bay resorts and casinos on the Las Vegas Strip, in a deal valuing the properties at $4.6 billion.

The deal, first reported early Tuesday by The Wall Street Journal, values MGM Grand’s real-estate assets at about $2.5 billion and Mandalay Bay’s at just over $2 billion.

Blackstone...