Strategic owns and manages a portfolio of 18 upscale hotels, including the JW Marriott Essex House in New York, the Four Seasons hotel in Washington, and the Marriott Hamburg in Germany.
The Blackstone offer "creates significant stockholder value with a high degree of execution certainty," said Raymond Gellein, chairman and chief executive of Strategic, in a statement.
Blackstone will pay $14.25 per share for Chicago-based Strategic and also pay $14.25 per units Strategic does not hold in a subsidiary, Strategic Hotels Funding LLC.
All told, including debt acquired, the deal is worth about $6 billion.
The offer price represents a 13 percent premium over Strategic's intraday trading price on July 23, when media reported a potential deal in the works.
"We are excited about the opportunity to acquire one of the highest quality luxury hotel portfolios in the US. As long-term investors in the lodging industry, we remain confident in the fundamentals of the sector despite recent market volatility," Blackstone co-head of US acquisitions, Tyler Henritze, said in the statement
Blackstone's real-estate portfolio includes hotel, office, retail and industrial properties in the US, Europe, Asia and Latin America, among them Hilton Worldwide and Chinese shopping malls SCP.
Strategic said that the transaction was expected to be completed by the first quarter of 2016.
Shares in Strategic opened 3.45 percent higher at $14.06, while The Blackstone Group gained 2.5 percent at $34.51.