BANGOR, Maine — The historic Merchants Bank Building, the one with the iconic curved facade along Broad Street in Bangor’s downtown, could finally open its doors again after nearly 15 years of vacancy.

Bangor city councilors on Monday night unanimously approved an agreement with a group called 25-27 Broad St. LLC, which has acquired the property.

It’s not yet clear what the developer plans to do with the site, but it will involve some sort of “commercial space” on the first floor, with the top three floors being converted into apartments, according to Tanya Emery, director of community and economic development for the city.

Emery said the developer is still ironing out plans for the site and there will be a substantial amount of work ahead to prepare the building for occupancy.

“The condition of the building is very stripped down,” Emery said.

The site, shaped like a generous slice of pie, was supposed to become Bangor Museum and History Center’s new home after philanthropists Bill and Sally Arata of Veazie donated the building nearly a decade ago.

The former Merchants Bank Building was built in 1835 as part of the old Circular Block, designed by architect George Pickering, for whom the nearby square is named. It survived two fires, including the Great Fire of 1911, and has been partially renovated numerous times over the past several years.

The Aratas bought the building in the early 1980s and leased it to various tenants through the years, including Cormier’s, a men’s clothing retailer. It has been empty since 2000.

After the Aratas donated the building in 2005, the museum began planning its move from its cramped headquarters — then at 6 State St. — to its larger Broad Street space.

The effort to whip the 12,000-square-foot, four-story building into shape, however, proved too much for the nonprofit organization. After five years and raising, then spending, nearly $3 million, the museum’s board realized the building needed significantly more work than anticipated.

The board’s former president explained that unexpected structural and architectural challenges, including for security measures and updates to the heating, ventilating and air conditioning system arose during the course of the project. The museum estimated it would need another $3 million to get the project done, but the staggered economy in 2009-2010 would have hindered further fundraising efforts.

However, the building did get a new roof, new windows, reinforced steel beams and more during that process.

Years after the museum project was abandoned, the building was sold to the developer. The asking price was around $300,000.

Emery declined to say who was behind the 25-27 Broad St. LLC, as the developer has chosen to stay behind the scenes in the early stages of the project.

To get the deal done, city officials have worked out a tax incentive with the developer. Under this agreement, the city would rebate 75 percent of the tax increment revenues paid on the property for the next five years, after which that rebate would expire. Emery said that agreement helped to close a funding gap for the project that might have held up rehabilitation and left the building vacant longer.

While the building was owned by the history center, a nonprofit, the city didn’t collect any taxes on it, and Emery said the city would be pleased to get it back on the tax rolls.

“The city really wants this building to be completed and it’s in our best interest,” she said.

Emery said she hopes the project will prove to be “further evidence that downtown Bangor is a great place to invest and a great place to grow.”