Glaxo has extended multiple buyout offers since April to both the HGS board of directors and its shareholders that valued the company at $2.6 billion, or $13 per share, but the company repeatedly rejected them as too low.
This latest agreement will fetch $14.25 per share in cash for HGS, a transaction value worth about $3.6 billion on an equity basis, or approximately $3 billion net of cash and debt, the companies said.
The deal brings an end to what had become an increasingly heated battle for control of the company.
Glaxo had attempted to bypass the board and purchase stock directly from investors. HGS then thwarted that effort with a poison pill, but gained a lawsuit from some disgruntled shareholders in response.
The two firms are development and marketing partners on several drugs, including Benlysta, which was approved by the Food and Drug Administration last year to treat systemic lupus.