Brazil will require international arrivals to show proof of vaccination against COVID-19 and for unvaccinated travellers to quarantine for five days.
The decision issued by a Supreme Court judge on Saturday invalidates regulations previously announced by the National Health Agency that required only a negative PCR test for visitors.
The fresh ruling goes against the wishes of President Jair Bolsonaro, who is still unvaccinated.
Bolsonaro had previously prevented the health agency from demanding proof of vaccination from visitors ahead of the world-famous Rio carnival.
Last week, the Brazilian president likened the vaccine requirement to "a dog collar" and questioned why it should be imposed on the Brazilian people.
The latest ruling is seen as another defeat for Bolsonaro, who has repeatedly undermined efforts to control the spread of the coronavirus, despite Brazil being one of the world's hardest-hit countries.
However, it is unclear how effectively Brazil can or will track those required to quarantine.
Travellers coming to Brazil will still need to submit a negative PCR test result before boarding in their country of origin and submit a declaration to the country’s health regulator.
Unvaccinated travellers will have to take a new virus test after the five-day quarantine period and must check in with a health agency centre that will have their addresses.
Meanwhile, city officials in Rio announced last Thursday they will go ahead with New Year's celebrations, despite fears the celebrations could become a super-spreader event as tens of thousands of people gather around the city to watch the fireworks.
Rio's mayor, Eduardo Paes, reminded people that "it is mandatory to present vaccination passports in bars, restaurants, and hotels", a measure strongly criticized by Bolsonaro.
Health officials and municipal authorities feel confident that limiting transportation to areas like Copacabana Beach can limit crowd size and avoid mass COVID-19 contagion.
More than 616,000 people have died of COVID-19 in Brazil, the country with the second-most deaths from the disease.
The pandemic has waned in recent months and the nation's seven-day average is approaching 200 deaths a day.