Omnicom has won AT&T's consolidated creative, digital and media accounts following a review that kicked off in June.
As such, the network's agencies will now have a remit to create work for a large portion of the telecom giant's US creative, media, digital and data offerings, however AdAge has reported that a spokesperson also said the win would include Mexico also.
The closed review pitted Omnicom against rival WPP, and the outcome means that incumbent ad agency BBDO is poised to retain the company's creative business, while the recently-formed Hearts & Science media agency will be the firm's new media agency of record.
WPP-owned Grey had previously worked with AT&T on its DirectTV brand, while WPP's MEC had worked on the brand's media account.
Last year, AT&T tapped former BBDO managing director Fiona Carter to head up its brand marketing team; signifying the close links between the duo.
AT&T senior executive vice-president and global marketing officer Lori Lee said in a statement that the the company believed the integrated "best in-class approach" was "the future for brands wanting breakthrough marketing innovation, quality and efficiency at scale."
"It was a thorough and thoughtful evaluation, and a tough decision because both firms presented outstanding ideas and both have done terrific work for us in the past. We thank them both for their efforts. We have selected Omnicom via its BBDO and Hearts & Science units to be AT&T's integrated creative and media agency," she added.
A WPP spokesperson told AdAge that the holding giant was "disappointed" was the decision.
In a separate statment, Grey said: "We have had a fantastic run on DirecTV and have been privileged to help grow that brand with years of award-winning campaigns that struck a chord in pop culture. We wish AT&T and their agency partners continued success."
The mammoth review is one of the biggest to occur in recent history, with the most recent figures from Kantar Media indicating that AT&T and DirecTV combined spend close to $800m on measured media in the states each year.