Pole Robert Kubica, who drove for Williams in 2019, will take up a reserve role at Alfa Romeo for 2020.
The 35-year-old, who recovered from a near-fatal rally crash in 2011 to return to motorsport’s top tier, will be back-up to Kimi Raikkonen and Antonio Giovinazzi.
Kubica’s arrival coincides with a deal for Polish petrol company PKN Orlen to become a title sponsor to the team.
“This team holds a special place in my heart and I am pleased to see some faces still here from my years in Hinwil,” said Kubica.
“Time and circumstances are obviously different, but I am convinced I will find the same determination and hunger to succeed.
“I am looking forward to helping Alfa Romeo Racing make the next step forward.”
Kubica scored one point last season and was comprehensively outpaced by team-mate George Russell.