Gov. Dannel Malloy announced on Tuesday that Alexion Pharmaceuticals, a multibillion-dollar drug company, will relocate its headquarters to New Haven’s planned Downtown Crossing development at 100 College St. with financial assistance from the state — adding hundreds of jobs to the Elm City.

Malloy’s announcement marks the state’s latest bid to foster biotechnology and medical science industries in Connecticut. Alexion’s relocation is aided by $51 million in tax credits, loans and grants administered through the Department of Economic and Community Development. Currently based in Cheshire, Conn., Alexion will move 350 of its current employees to New Haven and make an additional 200 to 300 new hires at the new facility by 2017, Malloy’s office said in a press release.

“Fast-growing companies like Alexion are true engines of economic growth — they attract investments, spur production and jobs in other industries, and improve our overall economy,” Malloy said in the press release. “Their decision to grow here in our state is a major step forward in our larger strategy to establish Connecticut as a world-renowned life sciences hub.”

The move would also make Alexion the central tenant of New Haven’s Downtown Crossing redevelopment, which will replace sections of Route 34 with urban boulevards and erect a 10-story, 400,000-square-foot medical office tower in the cleared space. The $100 million project was approved by the Board of Aldermen’s joint finance and legislation on June 14, and the full board is expected to hold a final, critical vote on the plan during its Aug. 6 meeting.

The move to 100 College St. will not be Alexion’s first foray in the Elm City area — the company was founded in 1992 as a small startup in New Haven’s Science Park. And the company’s founder and CEO, Leonard Bell MD ’84, worked as an assistant professor at the Yale School of Medicine and an attending physician at Yale-New Haven Hospital before starting Alexion. Bell remains on the medical school faculty as an adjunct assistant professor.

“We appreciate the governor’s vision to support the continued growth of New Haven as a major biopharmaceutical hub that will bring hope to patients, innovation to the industry and drive economic growth in New Haven,” Bell said in the press release. “By combining our research, operational and administrative headquarter functions into a single, state-of-the-art facility within the vibrant New Haven community we will maximize the efficiency of our organization while remaining in Connecticut.”

Alexion has a market capitalization of over $18 billion, and the company operates in over 30 countries around the world.