Miguel Oliveira said it was "extra special" to win his home MotoGP race in Portugal on Sunday for a dream finish to the season.
Jack Miller's second place in the Algarve ensured that Ducati sealed the constructors' title.
Oliveira followed up his maiden victory in Styria in August by taking the title under bright blue skies at Portimao in what was his first race in the premier class in his home country.
"It's unreal," said Oliveira afterwards. "You dream about these kinds of races and to finally be able to do it is incredible. I have no words to describe it, just my thanks to all the people and the crowd watching at home that couldn't be here today. To them I say thank you and to my team as well.
"It's a great day and a huge accomplishment for me. It's extra special because my family didn't get to see my first win live but they are here today so it's an incredible day for me, very emotional. I'm just glad to finish the season on such a high."
The KTM Tech 3 rider's triumph means there was no record-breaking 10th race winner, with Fabio Quartararo, Brad Binder, Andrea Dovizioso, Franco Morbidelli, Maverick Vinales, Danilo Petrucci, Alex Rins and already-crowned champion Joan Mir making it nine victors at the end of a highly unpredictable World Championship.
Morbidelli came out on top of a six-way battle for the runners-up spot, despite being pipped to second place on the last lap by Australian Miller.
Italian Morbidelli finishes in the overall standings 13 points behind Mir, who had confirmed his first world title in Valencia last weekend.
- 'Good movie' for Rossi -
Miller's strong finish meanwhile ensured Ducati claimed the constructors' title for the first time since 2007 at the expense of Suzuki, whose hopes were dashed after a disappointing weekend for Mir.
Mir started the race in 20th and had to retire due to electronic problems but the Spaniard will not worry too much, having already become the first Suzuki rider to be crowned champion since 2000.
Rins took third place overall and Vinales fourth, meaning Spain boasted three of the championship's top four. Frenchman Quartararo, who won the first two races of the season, ended up eighth.
Portimao was hosting the country's first race in the championship since 2012, with Oliveira already posting a record time in qualifying on Saturday.
He started in pole position and led all the way through to complete a fairytale victory, the only shame being that there were no fans in the Algarve to see it.
Oliveira still celebrated by carrying a Portuguese flag around his lap of honour.
Former champion Valentino Rossi, meanwhile, continued a disappointing end to the season for Yamaha by finishing 12th, in what was Rossi's final appearance before he switches to the satellite team in 2021.
The veteran Italian described his two spells with Yamaha as "divided into two parts – almost like a good movie".
The 41-year-old won four of his seven elite class titles with Yamaha after three with Honda.
However, his two-year spell with Ducati in 2011 and 2012 was ill-starred.
"After two bad years with another factory, when I was already getting old by MotoGP standards, I was desperate," said Rossi.
"I will never forget the moment when Yamaha told me I would have a chance to come back here.
"I'll always be thankful for that moment, because maybe I could also have stopped riding at that time if I wasn't able to come back here."
Britain's Cal Crutchlow was also bidding farewell to his full-time MotoGP career. He enjoyed a bright start but faded, dropping back to 13th.
Australian Remy Gardner secured his first Moto2 victory in Portimao with Italian Enea Bastianini crowned 2020 world champion.
Spaniard Raul Fernandez won the Moto3 race with compatriot Albert Arenas taking the title after he finished 12th in a thrilling finale to the season.