"We gave Valtteri a big challenge this year: joining the team at the 11th hour, stepping up to the forefront of F1 and pairing with the sport's best driver as his team mate", said team boss Toto Wolff in a statement.
Despite his good form, Mercedes seemed hesitant on whether it would keep Bottas next year.
The 28-year-old is third in this year's drivers' championship with two wins from 13 races. With that in mind, his results have been probably even more impressive.
"For our team, the bonus factors are the respect and sportsmanship that have grown between our two drivers", Wolff said.
Prior to joining Mercedes, Bottas had never won a race and had achieved nine podium finishes, a figure he has already matched this season.
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They were seen at TIFF on Sunday, for the premiere of The Breadwinner, an animated film produced by Jolie. "They ask the questions we're all asking".
"I've been very impressed by the mentality, commitment and the team spirit this team holds".
"The chemistry and dynamic between Valtteri and Lewis works and are what we need to take the fight to our competitors".
"Partnering Lewis has also been really good, and I'm enjoying the respect we have and the will to push this team forward together".
"I'm happy to have celebrated my first race wins in a Silver Arrow".
"However, there's always room for improvement and I still have not shown my full potential".
Bottas, who spent four seasons at Williams before his switch to Mercedes, secured his maiden pole position at the third round of the championship in Bahrain before landing his first win one race later in Russian Federation. "I will continue to work hard on and off the track, to further improve my driving, get even better results and show that putting their trust in me was the right decision".
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