The US Supreme Court has struck down a 2013 Texas abortion law that imposed restrictive regulations on the procedure.
The law requires doctors who perform abortions to have admitting privileges at nearby hospitals and clinics to maintain hospital-like conditions.
Republicans contended the law protects women while advocates argued the measures restricts access to abortions.
The key decision is the first major abortion ruling since 2007.
Justice Anthony Kennedy sided with the court's liberals in the 5-3 decision, which marked the first time the High Court has limited state abortion legislation in more than 15 years.
Nearly a thousand people gathered in front of the Supreme Court in the hot sun, holding signs and dancing to a Beyonce-heavy playlist.
At times, the pro-choice crowd's loud music and shouting drowned out chants of "we are the pro-life generation" from the other side.
But when the Court handed down its decision invalidating Texas' abortion laws, those who say they fight for life took to the microphones outside the court to say they would not give up.
"Women were hurt today," one said. "There are two victims to abortion, and my heart is breaking."
A few feet away, women holding "keep abortion legal" and "The burden is undue" signs danced, screamed and sang in reaction to the court's decision, many of them in disbelief - several had feared a tie.
The last time the top court issued a ruling on a major abortion case was nine years ago in a 5-4 decision to uphold a federal law banning a late-term abortion procedure.
The Supreme Court legalised abortion nationwide in its landmark 1973 Roe v Wade ruling.
The typically nine-justice court was one member short after the death of Justin Antonin Scalia earlier this year.
Chief Justice John Roberts, Justice Clarence Thomas and Justice Samuel Alito dissented.
