In one of the biggest telecom acquisitions in years, the cable giants Charter Communications and Cox Communications have agreed to merge in a $34.5 billion deal.

Charter is the second largest cable company in the U.S. after Comcast, while Cox is also among the largest with six million subscribers. Combining the two companies would create a cable behemoth, with enormous scale in both broadband internet connectivity and video.

Charter’s footprint includes New York City and Los Angeles, while Cox is a major player in cities like Boston, Phoenix and New Orleans. Assuming the deal closes, the combined company will be led by Charter CEO Chris Winfrey, with Cox CEO Alex Taylor serving as board chairman. The company would be called Cox Communications, with Spectrum being the brand that it uses for its consumer-facing business.

During a morning analyst call, Winfrey elaborated that Charter in adding Cox would secure additional...