By Dana Rubinstein

5:15 a.m. | Mar. 16, 2016

By the time Mayor Bill de Blasio’s citywide ferry service is up and running, one of the relics of the city’s ferry heyday will have finally been converted into a hotel.

The landmarked and long-underused Battery Maritime Building in lower Manhattan will open to the public as a hotel, restaurant and event space by the end of 2017, thanks to an infusion of cash from a new developer, according to the details of an agreement the de Blasio administration is hashing out with Stoneleigh Capital.

Connecticut-based Stoneleigh has signed a letter of intent with the Economic Development Corporation to replace the Dermot Company, which won the original 2006 Bloomberg administration bid to redevelop the building, but was never able to come up with the funding to cover rising construction costs and other “unforseen conditions,” according to the city.

At the moment, the renovation of the building is 55 to 60 percent complete.

Representatives from Dermot didn’t respond to a request for comment. Nor did representatives from Stoneleigh, which shares senior leadership with PLM International, whose website describes it as “a platform for its management and equity owners to make private equity investments in basic industry, real estate, and financial services.”

Stoneleigh’s plan for the building is only slightly different from Dermot’s.

Dermot planned to build a roughly 70-room boutique hotel, complete with a large rooftop restaurant and bar, and to renovate the Great Hall as a public and event space.

It was supposed to be done by mid-2015.

Stoneleigh intends to cut the size of the restaurant in half to allow for more hotel rooms and push back the completion date to the end of 2017.

“This new agreement will provide a clear path to restoring this beautiful landmarked building, as well as better utilization of the Great Hall,” said EDC spokesman Anthony Hogrebe, in a statement.

It’s not clear how much Stoneleigh plans to invest in the project.

The four-story Beaux-Art building neighboring the Whitehall Ferry Terminal is a beloved relic of a time when ferries served as a vital means for transportation between boroughs. It was completed in 1909 and was known for years as the Municipal Ferry Pier.

Today, a small portion of the building is used as the launch point for ferries to Governors Island.

“It’s the last significant piece of waterfront development, except for maybe the Seaport, that’s on the horizon,” said Jessica Lappin, president of the Downtown Alliance.