Holders of at least 99 percent of shares in Orbital ATK voted to approve the merger during the Wednesday meeting, the company said Wednesday.
Northrop will pay $7.8 billion in cash and assume $1.4 billion in net debt from Orbital ATK under the deal originally announced in September.
The transaction represented approximately 79 percent of Orbital ATKs total outstanding shares as of Oct. 10.
David Thompson, president and CEO at Orbital ATK, said the merger seeks to advance technology innovation and product development in support of clients missions, provide career opportunities to employees and create value for stockholders.
Orbital ATK expects to close the transaction in the first half of 2018, subject to regulatory approvals.