The court upheld the legality of a 2014 New Jersey law permitting sports betting at casinos and racetracks in the state and voided the federal Professional and Amateur Sports Protection Act. Some states see sports betting, like lotteries, as a potentially important source of tax revenue.
The Supreme Court justices struck down the entire federal law on a 6-3 vote, with Justices Ruth Bader Ginsburg, Sonia Sotomayor and Stephen Breyer dissenting.
"The legalization of sports gambling requires an important policy choice, but the choice is not ours to make. Congress can regulate sports gambling directly, but if it elects not to do so, each state is free to act on its own," Justice Samuel Alito wrote in the majority opinion.
The state law at issue would allow people age 21 and above to bet on sports at New Jersey casinos and racetracks but would ban wagers on college teams based in or playing in the state.
"Today's ruling will finally allow for authorized facilities in New Jersey to take the same bets that are legal in other states in our country," New Jersey Gov. Phil Murphy said in a statement. "I look forward to working with the Legislature to enact a law authorizing and regulating sports betting in the very near future."
Allowing sports to legalize sports betting is great news for investors in both professional sports teams and the gambling industry, billionaire Mark Cuban told CNBC on "Squawk Alley."
"I think everyone who owns a top four professional sports team just basically saw the value of their team double," said Cuban, owner of the NBA's Dallas Mavericks.
The ruling takes the U.S. a step closer to legal sports betting in numerous states, possibly even nationwide. Currently, the practice is legal only in select places such as Nevada, home to the gambling capital Las Vegas. While Nevada's Gaming Control board reported $4.8 billion in sports bets last year, the black market total is considered to be many times the legal market.
Americans wager "$150 billion illegally each year through off-shore, black market bookies," DraftKings CEO Jason Robins said in a statement. The fantasy sports company has nearly 10 million customers across the country. After the ruling, DraftKings announced plans to launch a mobile platform for sports betting to tap into the new market.
"States are now free to allow their residents to place mobile sports bets with licensed, trusted companies based in the U.S. and that pay taxes here," Robins said.
Shares of several casino companies moved higher following the ruling, including Caesars Entertainment, up 6 percent and Penn National Gaming, up 4 percent. Others gaining included MGM Resorts, Boyd Gaming and Churchill Downs. Wynn Resorts stock recaptured some of its losses from earlier in trading, down 1.9 percent on the day.
Industry analysts have said that dozens of states might legalize sports betting if they are not barred from doing so by the federal law. While awaiting Monday's ruling, seven states — Connecticut, Delaware, Pennsylvania, Iowa, New York, Mississippi and West Virginia — had laws prepared to make sports betting legal. Thirteen other states — California, Illinois, Indiana, Kansas, Kentucky, Maryland, Massachusetts, Minnesota, Michigan, Missouri, Oklahoma, Rhode Island and South Carolina — have plans or proposals to consider legalizing sports betting.
The most recent Summer Games in Rio de Janeiro was the first Olympics in 15 years where Americans could places bets, if you were in Nevada. The Rio Olympics drew "about half of average [NFL] Sunday game" in bets, Vice Fund senior portfolio manager Jordan Waldrep told CNBC, but that could quickly change for the Tokyo Olympics in 2020.
"The big events ... [are] what everyone's going to be paying attention to," Waldrep said. "What they really want is a situation where there's some unpredictability, like a great Australian swimmer going against a great U.S. swimmer. What the betting market needs is competitive events."
"Tokyo is trying to take advantage of it because there is going to be a massive influx of people," Waldrep added.
Multiple professional sports leagues, as well as the National Collegiate Athletic Association, were challenging the New Jersey law: Major League Baseball, the National Football League, the National Basketball Association and the National Hockey League.
"Today's decision by the United States Supreme Court will have profound effects on Major League Baseball," MLB said in a statement. "As each state considers whether to allow sports betting, we will continue to seek the proper protections for our sport, in partnership with other professional sports."
The ruling's implication for college sports is unclear, according to the NCAA. The organization said it is reviewing the decision.
"We will adjust sports wagering and championship policies to align with the direction from the court," NCAA chief legal officer Donald Remy said in a statement.
– Reuters contributed to this report.