Russian and Belarusian athletes will be permitted to compete in World Aquatics events with their respective uniforms, flags and anthems.
Competitors from both countries were banned from international events following Russia's invasion of Ukraine in February 2022. Belarus has served as a key staging point for the invasion.
However, some of their athletes competed as neutrals in the Paris 2024 Olympics as the restrictions were eased.
World Aquatics said more than 700 screenings had been conducted on athletes holding Russian and Belarusian sport nationality under its eligibility guidelines.
It added that such athletes will only be cleared to compete after successfully passing at least four successive anti-doping controls and completing background checks.
"Over the last three years, World Aquatics and the AQIU (Aquatics Integrity Unit) have successfully helped ensure that conflict can be kept outside the sporting competition venues," WA President Husain Al Musallam said in a statement.
"We are determined to ensure that pools and open water remain places where athletes from all nations can come together in peaceful competition."
In December, restrictions were lifted for Russian and Belarusian youth athletes.
WA also said Russia and Belarus will resume full membership rights.
The next World Aquatics championships, including artistic swimming, diving, high diving, open water swimming, swimming and water polo, are to be held in Budapest in 2027.
