"I suffered great prejudice for being a woman and for hailing from Olympic sport," the former South American record-holder said.
"But I will show I'm competitive, being the first woman ever to be elected president in the history of the club is also making true a dream."
Flamengo is regarded as having around 30 million fans across football-crazy Brazil.
Amorim, who jumped into Flamengo's pool to celebrate her success, was set to succeed Márcio Braga, a businessman who crowned his eighth presidential mandate at the club with a Brazilian championship title on Sunday.
Current Flamengo vice president Delair Dumbrosck, the candidate backed by Braga, was second in the election, with 699 votes.
The outgoing president, however, saluted Amorim's triumph: "She was the favorite and managed to confirm that at the polls. Patricia Amorim regards Flamengo as her second home, she has been going to the club since she was four and she has everything it takes to be a good president."
"This result also shows that Flamengo is once again innovating, by electing a woman to lead the club," Braga added.
Amorim – who took part in the 1988 Olympics in Seoul and is a mother-of-four – is set to take over the helm on January 1st, with a three-year mandate.
Patricia is also an elected councilor in Rio's city assembly. She promised to renew the contract of coach Andrade who conquered the Brazilian championship title.
"Now after this swimmer's celebration (jumping into the pool) I'm going home full of joy knowing tomorrow morning I will have to wake up concerned about how to pay for the players' salaries and who is going to be Flamengo's sponsor," said Patricia following her confirmation.
Mercopress