The news, confirmed during an Instagram broadcast on Saturday, follows the announcement that Alex Rins will also stay on for a further two seasons with the Hamamatsu marque.
Moto2 graduate Mir ended last year 12th in the standings with a best finish of fifth place at the Australian Grand Prix – though he battled the after-effects of a violent crash during the post-race Brno test, which forced him out of the Austrian and British GPs.
The Spaniard had been targeted by Ducati for its 2021 line-up, but Suzuki team boss Davide Brivio told Motorsport.com last month that everything had been agreed to retain Mir.
“I’m extremely happy to sign with Suzuki for another two years - renewing is the best thing that could happen and it’s a dream come true again,” Mir said.
“It’s really important for me to continue because now I have more time to learn and more time to show my potential.
“Two years can go by quickly, but I am ready to arrive at a higher level, and we are working every day to make that happen.
“I am also so pleased on a personal level because I have a really good team and crew around me. I really want to thank everyone at Suzuki for their confidence in me, and let’s see if I can get the results that we’re capable of.”
Suzuki is the second manufacturer to firm up its 2021 line-up, after Yamaha confirmed Maverick Vinales and 2019’s top rookie Fabio Quartararo on two-year deals.
Marc Marquez (Honda) and Tito Rabat (Avintia Ducati) are the only other riders with 2021 deals confirmed.