News of the $45.2-billion deal uniting the largest two US cable firms raised regulatory concerns about the reach of Comcast, which owns NBCUniversal's film and television assets and is one of the largest providers of cable Internet.
Comcast chairman and chief executive Brian Roberts said the plan would allow Comcast to deploy new technologies for delivering streaming content and use the internet cloud, with greater efficiency.
By combining, the companies said they could save $1.5 billion in operating costs while providing new services and products.
The mutually agreed merger is a triumph for Comcast over its rival Charter Communications, the nation's fourth largest cable operator, and Liberty Media Corp, its biggest shareholder.
The deal represents an offer of $158.82 per share, about $23 above where TWC has been trading and comfortably above Charter's offer of $132.50 a share, which was rejected as too low.
Comcast is already a dominant force in cable with nearly 22 million video subscribers.
Time Warner Cable, which was spun off as an independent company in 2009 from the Time Warner media-entertainment conglomerate, has 12 million.
The companies said their merger agreement is subject to shareholder approval and regulatory review.
But the news immediately raised concerns about the creation of a dominant force that spans cable, Internet and the content flowing over the networks.
Trefis analysts warned the combined company would command about 30% market share for cable.
Delara Derakhshani at Consumers Union said the merger "has the potential to be a very bad deal for consumers."
"This industry is notoriously unpopular with consumers due to poor customer service, not to mention ever-increasing bills, and a deal this size doesn't exactly convince us that things will get better," she said.
John Bergmayer at the consumer activist group Public Knowledge urged antitrust authorities and the Federal Communications Commission to block the deal.
He said an enlarged Comcast "would be the bully in the schoolyard, able to dictate terms to content creators, Internet companies, other communications networks... and distributors."Cable guy on steroids
Craig Aaron at the advocacy group Free Press said the deal would give Comcast a dominant share of the US pay-TV market and "triple-play" market for video, voice and Internet service.
"Americans already hate dealing with the cable guy... But this deal would be the cable guy on steroids — pumped up, unstoppable and grasping for your wallet," Mr Aaron said.
John Simpson at the activist group Consumer Watchdog said the deal "may be good for Time Warner's shareholders and Wall Street fat cats, but there is no way creating this media juggernaut can be considered in the public interest."
Comcast said that in order to address competition concerns, it is prepared to divest systems serving about three million subscribers, leaving a net gain of approximately eight million.
That would bring Comcast's managed subscriber total to roughly 30 million.New player in wireless?
Analysts said regulators may approve the deal but impose conditions.
"While we see no fundamental barrier to deal approval, conditions may be placed on the combined company to amplify and extend the types of conditions that were placed on the Comcast-NBCU deal in 2010 aimed at fostering online and video competition," said RBC Capital Markets analyst Jonathan Atkin.
The 2010 merger required Comcast and NBCU to sell content to other video providers at non-discriminatory prices, not discriminate against rivals through its set-top boxes and not take steps to restrict the distribution of its programs and films.
Geoffrey Manne, senior fellow at the technology think tank TechFreedom said competition concerns should be minimal because Comcast has already agreed to conditions in these areas for its NBCU acquisition.
"If anything, the merger will effectively provide consumers with more bargaining power to rein in overall programming costs and lower their bills," Mr Manne said.
Comcast shares fell 4.1% to $52.97 and TWC rose 7% to $144.81.