Gonçalves and Vassel followed in the footsteps of compatriots and two-time Olympic gold medallists Martine Grael and Kahena Kunze, who won the same title 14 years ago in the same waters.
“We finished the race and they came up to us so that was really nice,” said Vassel.
“We admire them so much, they’re amazing, and we are really happy to have accomplished the same as them.”
There was also plenty to celebrate for Poland and Italy, who both celebrated multiple gold medals.
Polish success came in the form of Stanisław Trepczyński in the iQFOiL male and Ewa Lewandowska and Julia Maria Żmudzińska in the 29er female.
Meanwhile, Italy continued on from the success of Quan Cardi and Mattia Tognocchi (ITA) on Thursday with victory for Mattia Cesana in the ILCA 6 male.
420 Female
Joana Faulhaber Tostes Antunes Gonçalves and Gabriela Vassel (BRA) sealed a gold medal on home water with back-to-back bullets.
The Brazilian pair entered the final day in the lead and secured top spot with victory in both of the final races to finish 22 points ahead of Maayan Shemesh and Emilie Louviot (ISR).
Maria Perello Mora and Marta Cardona Alcantara (ESP) finished second in both of the races on Friday but it was not enough to lift them onto the podium, with Kerkezou Iakovina and Giannouli Danai (GRE) holding onto bronze.
“We are really happy,” said Vassel. “We worked so hard to achieve this and it is an amazing accomplishment for us.”
iQFOiL Male
Stanisław Trepczyński (POL) sealed iQFOiL male gold in style, with three straight bullets to sign off the competition.
The Pole held a four-point advantage heading into the final day but ensured he would not be relying on anything but his own performance with victory in all three races.
It means he finished 14 points ahead of Leonardo Tomasini (ITA) and 35 ahead of bronze medallist Noé Garandeau (FRA).
The Frenchman held off the late challenge of Val Erzen (SLO), who just missed out on the podium in fourth despite coming second in all of Friday’s races.
“I am super happy,” said Trepczyński.
“The weather was absolutely blasting, windy all the time.
“This is my last youth competition so this gives me motivation to fight for senior titles.”
29er Female
Ewa Lewandowska and Julia Maria Żmudzińska (POL) were crowned 29er female champions despite no racing taking place on Friday.
The Polish pair led from gun to tape in Brazil after an electric start to the competition saw them win the first five races, establishing a lead that they never relinquished.
Sarah Jannin and Fleur Babin (FRA) took silver after claiming bullets in four of the last five races, eventually finishing 10 points behind the winners.
Bronze went to Boróka and Szonja Fehér (HUN), who finished four points ahead of Malena Rüegge and Liv Wicki (SUI).
ILCA 6 Male
Mattia Cesana (ITA) clinched gold in the ILCA 6 male class with a third-place finish in the final race of the competition.
Cesana knew he was all but assured the top place on the podium if he could replicate his strong form from throughout the week, and the Italian duly delivered to take victory by 15 points from Luka Zabukovec (SLO).
The final bullet of the competition went to João Portes (POR) who continued the impressive form that has seen a late surge up the standings, with victory in the final race enough to clinch bronze for the Portuguese sailor.
Portes pipped Hidde Schraffordt (NED) to the final medal as the Dutchman finished sixth on Friday, with Erik Norlén (SWE) taking second in the final race to rise to fifth overall.
iQFOiL Female
Kristyna Pinosova (CZE) sealed iQFOiL female gold with a trio of second-place finishes in Buzios.
Pinosova led the way heading into the final day after climbing ahead of Carola Colasanto (ITA) on Thursday.
The Czech made no mistake in sealing victory with a set of consistent showings to end up 16 points clear of Lina Erzen (SLO) in silver and Darcey Shaw (GBR) in bronze.
Emma Viktoria Millend (EST) had the best individual day on the water on Friday, winning both of the first two races before Erzen took the final race of the day to pip Shaw by a point.
The Brit could only finish seventh in both of the final two races but was still able to hold off Colasanto for the final place on the podium.
ILCA 6 Female
Roos Wind (NED) produced her fourth consecutive bullet to win ILCA 6 female gold.
Wind finished just four points ahead of Emma Mattivi (ITA) and a further point in front of Sienna Wright (IRL) at the conclusion of a dramatically close competition.
It was that trio that comprised the top three finishers in the final race, with Wright finishing second ahead of Mattivi.
That proved enough for the Irish sailor to take the final podium spot ahead of Petra Marendic (CRO), who could only finish ninth in the final race of the competition.
Formula Kite Female
Derin Atakan (TUR) was crowned Formula Kite female champion despite retiring from the only race of the day on Friday.
Atakan led throughout the week of competition and sealed gold after earning eight bullets across the four days of racing.
The Turkish sailor ended up three points ahead of Catalina Turienzo (ARG), who claimed victory in the final race with Ella Geiger (GBR) and Suofeiya Li (CHN) finishing second and third.
Turienzo comfortably took silver ahead of Mika Kafri (ISR) who finished 18 points behind in bronze.
29er Male/Mixed
Champions Hugo Revil and Karl Devaux (FRA) signed off from the 29er male/mixed class with a bullet in the final race of the competition.
The French pair opened the day with a pair of second-place finishes to put themselves in a commanding position for gold, before completing with a sixth and a victory to finish in style en route to their second world title.
“It feels really good,” said Devaux. “The conditions were really good, strong wind which we really like: it’s so cool.”
It meant they finished 16 points ahead of Alex Demurtas and Giovanni Santi (ITA) who earned silver, while Ben O’Shaughnessy and Ethan Spain (IRL) claimed bronze.
Demurtas and Santi took the day’s opening bullet before Zeb van Dorst and Michiel Dam (NED) claimed victory in the day’s second and third races.
Nacra 15
Daniel and Nora Garcia de la Casa (ESP) clinched a dramatic victory in the Nacra 15 class, leapfrogging overnight leaders Cody Roe and Brooke Mertz (USA) in the final race.
The Spaniards finished third in the last race of the competition to finish two points ahead of their American rivals, who finished seventh to slip down to silver.
Both crews finished just ahead of Marie Mazuay and Clément Guignard (SUI), who earned bullets in both of the day’s races to rise to third overall and snatch bronze ahead of Côme Vic-Molinero and Ylona Jaud (FRA) by four points.
Formula Kite Male
Max Maeder (SGP) claimed Formula Kite male gold after dominating the week of racing in Brazil.
Maeder won all but one of the 14 races to comfortably take top spot ahead of Qibin Huang (CHN), the only other sailor to win a race.
Huang finished 12 points behind Maeder after finishing second eight times, with Riccardo Pianosi (ITA) winning bronze.