Fallon Co.'s Fan Pier mixed-use project will span eight buildings on 21 acres.

BOSTON-Law firm Goodwin Procter has signed a letter of intent to anchor a new 500,000-square-foot build-to-suit tower at the Fallon Co.‘s Fan Pier mixed-use development on the Boston waterfront. The move to approximately 360,000 square feet of office space will bring more than 860 attorneys and staff to Fan Pier.

The announcement of the BTS for Goodwin Procter, which was founded in Boston a century ago, brings the number of Fan Pier high-rises either built or under development to five. Along with the Goodwin Procter building, one office tower is complete, two are under construction and groundbreaking is planned next year for the site’s first residential structure.

“Our vision for Fan Pier was to attract a broad mix of best-in-class businesses from recognized industry leaders to innovative start-ups,” says Joseph Fallon, Fallon Co.’s. president and CEO, in a release. “As an established, leading law firm with a rich history in Boston and forward-looking approach to business, Goodwin Procter is exactly the type of company we hoped to welcome to Fan Pier when we conceived this project and we look forward having them join us on Boston’s waterfront.”

Vertex Pharmaceuticals has also established an outsize presence at Fan Pier. By the end of 2013, it will occupy two 18-story towers totaling 1.8 million square feet that will serve as its global headquarters. When it’s completed, Fan Pier will encompass eight towers on 21 acres.