Mountain Development Corp. is hailing the lease-up of a 400,000-square-foot office building in Roseland, following a more than $40 million effort to reposition the property.

The owner and developer said last week that the property, 56 at Roseland, is near full occupancy after the completion of a recent 20,000-square-foot lease. MDC did not identify the tenant by name, but described it as a global consulting firm.

The deal prompted the company, part of a joint venture that owns the complex, to host a reception for tenants, bankers, brokers, design professionals, counsel and others who were involved in the repositioning effort. A crowd of more than 150 turned out to the campus at 56 Livingston Ave., which is anchored by law firms Connell Foley LLP and Lowenstein Sandler LLP.

“We were delighted to welcome another prestigious tenant to 56 at Roseland, and to celebrate with existing tenants and decided to utilize the occasion as an opportunity to say ‘thanks’ to everyone who has worked so hard to made this property such a success,” said Michael Seeve, president of MDC. “This is a building unlike any other. It’s more than just the contemporary office environments and the array of amenities. The elite tenancy has created a special, high energy environment for professionals who work on complex, exciting projects with dynamic clients and enjoy being surrounded by others with similar endeavors and practices.

“It makes for a very rewarding experience when so many high achieving people are gathered together. We could not be more proud of the accomplishments of the tenants.”

The repositioning, completed last year, sought to redevelop and modernize the building from its days as a headquarters for a single tenant, Organon International. That resulted in new amenity spaces, including a new on-site café with a 400-seat dining area and event space, a health club and wellness center with full lockers and shower facilities and security and concierge services.

Outdoor amenities include an exterior lounge area with fire pits, a green wall, hiking trails, volleyball court and walking paths, MDC said. The firm also touted technical features such as an optimized data center and support space.

The campus spans 56 acres off Exit 5B of Interstate 280, providing easy access to other major highways including interstates 287 and 80, the Garden State Parkway and New Jersey Turnpike. It also sits within two miles of downtown Livingston.