The deal is a continuation of the relationship between the 20-year-old and Renault/Alpine, Piastri having been part of the French manufacturer’s academy system for some time.
The role will include an “extensive testing programme” to help prep Piastri for an F1 race seat in 2023.
“I’m super excited to be joining Alpine F1 Team as reserve driver,” said the Australian. “I’m looking forward to being much more involved with the team and contributing to its intended success next season.
“The reserve driver role is the next step towards my aim for a race seat in 2023, which is very exciting.
“I’ve proved myself in the junior formulas over the last couple of years and feel like I’m ready for Formula 1 now; along with the trackside experience at race weekends, we will put together a substantial test programme in order to keep developing myself to grow even more prepared for a race seat.
“I’m very thankful to Alpine for their support. We’ve enjoyed two very successful seasons together in the Academy and I’m grateful for the faith they’ve put in me for this next step with an eye on a bigger future.
“My focus now is finishing the Formula 2 Championship in the best possible way with Prema and I’m looking forward to being back in the car and pushing hard on track.”
Piastri currently leads the F2 standings in what his rookie season in the second tier, following an impressive Formula 3 title win in 2020.
His run of consecutive title success stretches back to 2019 when he secured the Formula Renault Eurocup crown.
Piastri will replace Daniil Kvyat in the Alpine reserve driver role.
“Oscar’s natural talent is clear to see, so we’re very proud and privileged to have him as part of our team as our Reserve Driver from next year,” said Alpine CEO Laurent Rossi.
“Not only does Oscar have the on-track skills, as demonstrated over the last couple of years in the junior categories, but also the maturity and composure that makes him really stand out from the rest.
“The next step will be to consistently attend grands prix to fully integrate with the race team, learn what is expected of an F1 driver and be ready for when the opportunity comes.
“Oscar’s graduation highlights the success of our Alpine Academy and underlines its strength as one of the best young driver programmes in motorsport. We look forward to seeing our young talents continue to blossom through the years to come.”