Davos Congress Centre in the Alps now covers 12,000sqm and has three sections providing a plenary hall for 2,000, as well as a further 34 meeting spaces.
The venue holds the annual World Economic Forum, and has also provided space for Astra Zeneca and Wyeth Pharmaceuticals, said Destination Davos Klosters manager of business sales Markus Schiedeck.
"Congresses are growing more and more, but we had no space," he said. "We decided we had to invest before they left the destination."
Work took place over two years, with the centre closing during the summer months when business was quiet, but remaining open in winter.
The area is also renowned as the destination where Prince William and Kate Middleton's romance was first made public in 2004.