One of the most active developers in Greater Boston and a leading life science landlord are the new owners of General Electric’s future headquarters and a prime development site on Boston’s Fort Point Channel.

National Development and Alexandria Real Estate Equities’ $252 million acquisition on Thursday sets the stage for expansion of the Seaport District’s life science cluster, which kicked off with the 2014 opening of Vertex Pharmaceuticals’ global headquarters and has since attracted the headquarters of Alexion Pharmaceuticals and a Mass Innovation Labs accelerator.

“We think it’s one of the best sites in all of Greater Boston,” said Brian Kavoogian, president of Charles River Realty Investors, a private equity firm affiliated with National Development.

The development team intends to file plans with “very modest changes” from the 12-story, 293,000-square-foot office building that’s approved for GE, Kavoogian said.

The new headquarters was a cornerstone of former GE CEO Jeff Immelt’s attempts to reposition the industrial conglomerate as it moved its headquarters from Fairfield, Connecticut to Boston in 2016. GE leases office space on Farnsworth Street in Fort Point while renovations continue on two Necco Way warehouses, which will open this fall and serve as its new headquarters.

After GE pulled the plug on the new office tower plans, GE and MassDevelopment agreed to jointly market the 1-acre development site along with the Necco Way warehouses, which are owned by MassDevelopment. The combined properties total approximately 2.6 acres.

The $252 million proceeds, split between GE and MassDevelopment, ensure that the state will get repaid for $87 million in incentives it gave GE to move to Massachusetts and create up to 800 jobs.

The transaction is the biggest for a preapproved development site in the Seaport since WS Development paid $359 million for 12.5 acres in 2015. Those parcels were permitted for 2.8 million square feet of development.

“It’s a single-phase project so hopefully we are going to be under construction in a much shorter period,” Kavoogian said. “Between the timing, the size and the location, it justifies the price that we’re paying.”

Brendan Carroll, director of intelligence at Boston-based Perry Brokerage, said the site has multiple advantages reflected in the purchase price.

“It is in the Seaport, a favored geography for deep pocketed organizations, it’s in a special setting directly on the Fort Point Channel and offers the best proximity in the submarket to robust transportation alternatives, at South Station,” Carroll said.

Developers are making life science developments and conversions a major emphasis as the industry expands its Greater Boston footprint beyond Cambridge, Boston’s Longwood Medical Area and a handful of suburbs. Alexandria has been one of the region’s most active lab developers, with a 6.2 million-square-foot portfolio in Greater Boston including some of Kendall Square’s most valuable properties leased to companies including Bristol-Myers Squibb and Facebook.

This year it’s increasingly focused on South Boston and the Seaport District for acquisitions of development sites.

Along with Boston-based Anchor Line Partners, it’s proposing a 210,000-square-foot office and lab building at 99 A St. In April, Alexandria and National Development paid $81 million for the 657-space parking garage at 10 Necco St., which borders the GE property.

In a quarterly financial report, Alexandria said it’s planning a 175,000-square-foot development on the site. Kavoogian said plans are still in the early phases but the property will continue to have a substantial parking component.

“We think it will continue to serve as a parking garage, and we’re figuring out the extent of what we can do for additional development,” he said.

Newton-based National Development first partnered with Alexandria on development of Longwood Center in Boston, which broke ground in 2012 after Dana-Farber Cancer Institute signed on as anchor tenant.