He won a gold in the men’s + 90 kilogram beach wrestling final.
Rahmani beat Turkey’s Ufuk Yılmaz in the final and Mamuka Kordzaia from Georgia won a bronze medal.
Iran’s Fatemeh Sadeghi had previously won a silver in karate kata.
The World Beach Games include a total of 14 disciplines in 13 sports.
More than 1,200 athletes from 97 countries are taking part in the games, with action split between the Katara and Al Gharafa venues between October 12 and 16.