The $70 per share offer is a 51 percent premium above ImClone's closing stock price on July 30, the company said in a statement.
"This strategic combination will create one of the leading oncology franchises in the biopharmaceutical industry," the statement said.
ImClone's Chief Executive Officer John Johnson said the company was "excited about the possibilities of improving outcomes for for individual patients and building value for shareholders."
The combined arsenal of cancer treatments allows the merged company to "target a broader array of solid tumor types including lung, breast, ovarian, colorectal, head and neck, and pancreatic," the statement said.
Both company boards have approved of the deal, which trumps a previous offer from Bristol-Myers Squibb, which offered ImClone $62 a share for the company, the Indianapolis Star reported.