The Old Main Post Office may finally be ready to deliver.

Late tonight, the mayor's office announced that a deal had been finalized with 601W to redevelop the long-vacant, hulking site that straddles the Eisenhower Expressway on Chicago's front door to the west.

Mayor Rahm Emanuel, in a statement, touted what is projected to be a $500 million project with the promise of 1,500 jobs.

“Today we are taking another significant step toward transforming the Old Main Post Office site into an economic driver for the city of Chicago,” Emanuel said. “This project will create thousands of jobs and generate new economic opportunities for residents in our neighborhoods, while restoring and reviving an iconic gateway to our city. While today marks a milestone, there is still work to do, so I look forward to watching this important project continue to move forward in the months ahead.”

Final terms of the deal were not immediately available. The project, though, will be completed in three parts. The initial phase will focus on rehabilitation of the site, which has stood empty since the mid-1990s, with repairs to the windows and facade—a process projected to take 24 months.

The second phase will continue window and roof work, plus elevator refitting. The lobby and common tenant areas will be the final phase of work.

Pre-leasing will start in 2017, with initial occupancy targeted for 2018.

The mayor's enthusiasm comes despite two contentious months during which 601W's plans to buy the site had first been reported. Monaco-based owner Bill Davies had been under increasing pressure from the mayor's office to unload the 2.7 million-square-foot structure in the West Loop, with the threat of seizure by eminent domain becoming more pronounced.

In fact, the mayor's office had received the mid-March purchase news coolly, saying 601W should respond to an RFP along with other bidders. Bids had been due June 10—a process apparently no longer necessary.

“I am confident in 601W's ability to deliver on its plan and look forward to substantial progress in the months ahead,” 25th Ward Ald. Daniel Solis said in the statement.

Led by Mark Karasick, 601W is an experienced developer that has owned real estate throughout the U.S. The New York-based firm is known in Chicago as owner of the city's third-tallest building, the 83-story Aon Center, and its next-door neighbor, the two-tower Prudential Plaza.

“601W will reposition the building as an incredibly unique campus allowing companies seeking large, open layouts with plenty of light and air,” Karasick said in the statement. “The building's scale and architecture will allow us to provide spectacular amenities, green space and services no other building can provide. This project is ideal for companies seeking a new corporate headquarters, particularly suburban firms that could more easily attract professional talent to a vibrant location along the Chicago River that's easily accessed by train or car. “

The news was a late exclamation point on a day of big downtown redevelopment announcements. Earlier, a deal for Related Midwest to revamp a huge, 62-acre South Loop site stretching from Roosevelt Road to Chinatown was presented—a process projected to take 15 years and cost billions of dollars to complete.