Rahimi, who is based in Germany, said his aim in organizing "Afghanistan Fight 4 Peace" was to bring the people of his country together after decades of warfare.
Several hundred spectators watched the bout live in a large hall in the capital, cheering wildly when Rahimi won the vacant WBO intercontinental middleweight title. Mbelwa was unable to continue because of a shoulder injury.
Mbelwa had showboated in the early rounds, but retreated to his corner holding his shoulder in the seventh after Rahimi delivered four fierce rights in quick succession.
Rahimi's supporters carried a banner reading "We Want Peace" during the match. Spectators crowded into the ring after the match to congratulate both fighters.
"I am very happy because this victory belongs to all Afghans," Rahimi said.
The boxer has lived in Germany since childhood when his parents moved there in 1992. He has won 22 of his 23 pro fights.
Organizers said the two men made history by staging the first professional match in Afghanistan. But amateur boxing is popular in Afghanistan and the nation's first Olympic boxer, flyweight Ajmal Faisal, took part in the London Games this year.
The fight was the latest of several sporting events which authorities hope will help unite the nation.
Earlier this month, Afghanistan's new football league held its first national championship at Kabul's renovated Ghazi stadium.
In September, the country's cricket team participated in the World Twenty20 tournament in Sri Lanka, where they were eliminated after losing to India and England.