Robert Kubica will serve as Alfa Romeo's reserve driver for the 2020 season.
Kubica returned to the top level of motorsport in 2019 after eight years away, having suffered a massive rallying crash in 2011 that left him with a partially severed arm.
The Pole partnered George Russell for an uncompetitive Williams car, Kubica claiming its sole point of the season as the team almost exclusively occupied the back row.
Outqualified by Russell at all 21 races, Kubica was replaced by Nicholas Latifi at Williams for 2020.
However, he will return to the team that gave him his F1 bow in 2006. Kubica made his debut when the team was known as BMW Sauber and he claimed a pole in Bahrain and a win in Canada for it in 2008.
Kubica's return was revealed in an announcement confirming Polish petroleum company PKN ORLEN will link-up with Alfa Romeo as a title sponsor.
Team principal Frederic Vasseur said: "The exciting new partnership with PKN ORLEN is a statement of intent for both parties.
"It is proof of the ambition of our common project and of our desire to compete at the very top of Formula One.
"We are also delighted to welcome Robert back home and we cannot wait to start working with him.
"He is a driver that needs no introduction: one of the most brilliant in his generation and one who displayed the true meaning of human determination in his fight to return to racing after his rallying accident.
"His feedback will be invaluable as we continue to push our team towards the front of the grid."