The competition watchdog has officially approved BT's £12.5 billion buy out of mobile phone firm EE.
Authorisation from the Competition and Markets Authority (CMA) means the deal brings together the UK's largest fixed and mobile telecoms businesses.
It comes after the merger was provisionally given the green light in October last year.
Telecoms giant BT announced in February last year that it had agreed to acquire the firm.
Rivals have claimed the move would allow BT to "remonopolise" the UK telecoms sector, forcing broadband firms to use its old network.
But John Wotton, who chaired the inquiry into the deal, said evidence "does not show that this merger is likely to cause significant harm to competition or the interests of consumers".
BT chief executive Gavin Patterson described the acquisition as "great news".
He said: "We are pleased they (CMA) have found there to be no significant lessening of competition following an in-depth investigation lasting more than 10 months.
"The combined BT and EE will be a digital champion for the UK, providing high levels of investment and driving innovation in a highly competitive market.
"I have no doubt that consumers, businesses and communities will benefit as we combine the power of fibre broadband with the convenience of leading edge mobile services. I look forward to welcoming EE into the BT family."
Following Friday's approval, BT will commence the formal process of completing the deal. A prospectus will be issued in the week commencing January 25 with the deal set to close on January 29 when Deutsche Telekom and Orange will receive shares in BT.
The telecoms giant will post its third-quarter results on February 1.
The deal is expected to be completed before the end of March.