Liberty Bay Credit Union signed a lease for space in a 4-story, 89,466-square-foot office complex in Braintree.

The 31,130 square feet of space at 300 Granite St. will house its corporate headquarters and primary banking branch on the building’s third and first floors. The credit union was previously in an adjacent building at 350 Granite St.

The building is located at the intersection of Routes 128 and 3, immediately adjacent to the South Shore Plaza.

The space opened up following Fidelity Investments’ departure, which opened up 46,334 square feet. Following Liberty Bay’s lease, existing tenant Altra Industrial Motion Corp. renewed and expanded its corporate headquarters on the second floor to absorb the remaining footage.

Liberty Bay was represented by Michael Frisoli and Peter Whoriskey of Newmark Grubb Knight Frank.

Robert Byrne and Chris Mullen of Transwestern represented building owner Sun Life Financial Inc.