Texas, along with 19 states, had argued to U.S. District Judge Reed O'Connor that they had been hurt by a jump in the amount of people utilizing state-backed insurance. His ruling is expected to be appealed, which means the conservative-majority Supreme Court, with newly appointed Justice Brett Kavanaugh, will have a chance to reassess the constitutionality of the law.
Twenty Republican-led states brought the lawsuit.
Lawyers for the Department of Justice had suggested that O'Connor should not rule until after the open enrollment period for the 2019 plan year ends on December 15 in order to avoid disrupting the markets.
"If this Texas decision on the ACA is upheld, it would throw the individual insurance market and the whole health care system into complete chaos", Larry Levitt, a senior vice president at the Kaiser Family Foundation said on Twitter.
The lawsuit, which was created to kill ObamaCare, is supported by President Trump.
President Trump celebrated the decision, calling it "Great news for America!".
President Donald Trump tweeted on Friday, "As I predicted all along, Obamacare has been struck down as an UNCONSTITUTIONAL disaster!"
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Earlier in 2018, Salah won the English double - the Players´ Player of the Year and the Football Writers´ Player of the Year. But Owen is a fan, saying on BT Sport: "I think the manager has to take some of the blame - the system, the way he plays".
O'Connor said that because the individual mandate is "essential" to the rest of the ACA, all of Obamacare is invalid. The judge's ruling will also be immediately appealed.
Democratic leaders, meanwhile, reacted harshly to the decision.
Seema Verma, the administrator of the Centers for Medicare and Medicaid Services, told reporters in November that the administration had contingency plans in place for a ruling if the law was overturned, but declined to elaborate on them.
The move now threatens 20 million who rely on its coverage. Trump tweeted. "Now Congress must pass a STRONG law that provides GREAT healthcare and protects pre-existing conditions". "Today's misguided ruling will not deter us: our coalition will continue to fight in court for the health and wellbeing of all Americans".
In Texas alone, there are more than 4.5 million "nonelderly adults" with pre-existing conditions that could make it hard for them to get health insurance if Obamacare went away, statistics show.
Because the administration would not defend the law, California, joined by 16 other Democratic states, stepped in.
The ACA can only stand as it was originally designed by Congress, O'Connor added, saying that lawmakers needed to have the penalty to force people to sign up for exchange insurance.
Information cards displayed during an Affordable Care Act enrollment event in San Antonio, Texas, in 2016.