The deal will create the second largest cable broadband provider in the US.
Charter had to agree to not stop its content providers from separately selling shows online, as part of the approval.
The deal also still needs approval from the Federal Communications Commission (FCC) before it can go ahead.
But the head of the FCC Tom Wheeler said he was seeking approval for the deal, noting the merger conditions "will directly benefit consumers by bringing and protecting competition to the video marketplace and increasing broadband deployment."
The DoJ said it would work with other regulators to ensure the merger did not "choke off" access to online videos.
"The settlement forbids the merged company, referred to as "New Charter," from entering into or enforcing agreements that could make it more difficult for online video distributors (OVDs) to obtain video content from programmers," the DOJ added.
US cable companies are facing stiff competition from online service providers such as Netflix, Amazon and Hulu, as customers increasingly choose to stream films and television shows over the internet often for a lower price.
Charter will pay $78bn (Â£54bn) for Time Warner and $10.8bn for Bright House.
The combined three firms will serve cable television and broadband to 23.9 million customers in 41 states.
The deal was announced last year after Comcast abandoned its $45bn plan to buy Time Warner Cable fearing pressure from regulators.

The 23-year-old, who was out of contract, is manager Paul Cox's ninth signing of the summer.
Hughes was a target for Cox in January, when he was at Cambridge United, but Barrow were unable to sign him either on loan or permanently.
He moved to Scotland in February and played 11 games for Inverness, nine of them in the Scottish Premiership.
But he only started five games and leaves Caley Thistle after the exit of manager John Hughes, who has been succeeded by Richie Foran, making the step up from club captain.
Hughes scored Cambridge United's opening goal when they beat Gateshead 2-1 to win the Conference play-off final at Wembley in 2014 and was part of the U's side that also won the FA Trophy that year.

It took some amazing photos of the dwarf planet and now scientists are hard at work looking through all the information it sent back.
Here's Newsround's rundown of the most interesting things we've discovered about Pluto so far from the New Horizons probe.
The high-resolution cameras on board New Horizons have shown Pluto to have a distinctive heart-shaped crater on its surface.
The shape is believed to have been caused by an impact at some point in the past.
One side of the heart is smoother than the other, and researchers believe the crater is filled with frozen gases from the atmosphere, including nitrogen, methane and carbon dioxide.
The first image released by Nasa showed Pluto to be reddish in colour.
But, this doesn't mean it's the same as the other famous red planet, Mars.
Both planets are red, but for different reasons, due to the ways chemicals react in their atmospheres.
New Horizons has provided more accurate information about Pluto's size, and we now know it's about 80km wider than previously predicted.
Nasa experts say it's around two-thirds the size of our Moon.
This means that Pluto is likely to be made up of less rock and more ice beneath its surface, according to members of the mission team.
One of the main things we learned is that Pluto does have a polar ice cap.
Scientists had thought this before but couldn't prove it until they saw the new images beamed back from the probe.
Temperatures on Pluto are extremely cold!
They range from -172 to -238 degrees Celsius depending on where it is on its orbit.
Experts had assumed that the dwarf planet was cooling but the new data shows that this isn't happening.
The New Horizons probe is 5 billion kilometres from Earth.
This means it can only send back its information to mission control in the US very slowly.
So, just one black and white picture of Pluto would take over three hours to transmit back to Earth.
Getting all the data from its flypast of Pluto last week will take almost 16 months.
So, we can look forward to lots more new discoveries about the far away dwarf planet over the next year or so.
The US Department of Justice (DoJ) has approved Charter Communications purchase of cable operators Time Warner Cable and Bright House networks.
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National League club Barrow have signed midfielder Liam Hughes from Scottish outfit Inverness Caledonian Thistle.
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The New Horizons probe successfully completed its fly-by of Pluto last week.