That clears the way for the deal to create Switzerland's second-biggest telecoms group behind Swisscom.
"Like Swisscom, UPC/Sunrise will have its own mobile and fixed network infrastructure. There is no threat of eliminating effective competition," the WEKO agency said, using the name of the Liberty unit making the deal.
"It cannot be assumed that UPC/Sunrise and Swisscom will coordinate in the future. Therefore, WEKO approves the takeover without any conditions or conditions," it said.
Sunrise said the deal was set to close in mid-November.
(Reporting by Michael Shields, editing by John Revill)