Buying Time Warner Cable and Bright House Networks will turn Charter Communications, a midsize cable company, into the country's No. 2 home Internet provider, after Comcast (CMCSA). The new Charter will be No. 3 in video, trailing Comcast and AT&T (T), which bought DirecTV last year.
Monday's OK comes with conditions meant to preserve competition and protect consumers.
The Federal Communications Commission and California's utility regulator also need to give permission before the deal can close. Both are expected.
Public-interest groups have protested industry consolidation, but opposition to Charter's deal was muted compared with the backlash in recent years to Comcast's failed bid for Time Warner Cable.
Both companies' shares rose more than 4 percent on Monday on the news. Time Warner Cable closed up $8.31 to $209.76, and Charter rose $9.10 to close at $207.01.