J&J is paying $280 a share in cash for Actelion, retaining the Swiss company's commercially available treatments for rare diseases such as an artery disorder known as pulmonary arterial hypertension.
However, Actelion will spin off its drug-discovery operations into a separate company called R&D NewCo, in which J&J will initially hold a 16% stake, with an option to acquire another 16%.
The takeover deal comes after J&J had a surprising a change of heart just before Christmas and re-entered acquisition talks with Actelion.
J&J had abruptly bowed out of the bidding process for Actelion earlier in the month after the Swiss firm said that it was “engaged in discussions with another party”.
Actelion had given no details about who the third party was, but press reports at the time suggested it was French firm Sanofi SA.
However, J&J said it had entered into “exclusive negotiations” to acquire the Swiss firm, indicating that other potential suitors had left the process.