Washington, D.C.-based Carr Properties has joined a union pension fund as an investor in One Congress, a planned 1-million-square-foot office tower at Boston’s Government Center garage property redevelopment known as Bulfinch Crossing.

Developer HYM Investment Group has been retained as project developer. HYM originally partnered with National Real Estate Advisors, a subsidiary of the National Electrical Benefit Fund, which has formed a joint venture with Carr Properties on One Congress. HYM is seeking an anchor office tenant to begin construction of the 43-story tower designed by Pelli Clarke Pelli Architects.

“Now that Carr is on board, we can begin the redevelopment of the existing parking garage which will be transformed into a residential, office, retail and hotel masterplan, bringing significant growth and vibrancy to this neighborhood,” HYM’s Managing Director Thomas O’Brien said in a statement.

The first phase of Bulfinch Crossing started in January 2017 with partial demolition of the 2,300-space parking garage to make way for a 45-story apartment and condominium tower designed by Boston-based CBT Architects.

The development will include six buildings including 800 residential units, a 200-room hotel and 82,500 square feet of retail space.

Carr Properties owns 17 office properties totaling 4.5 million square feet and five development sites totaling 2.4 million square feet in the Washington, D.C. area.