Robert Kubica will join the Alfa Romeo Formula 1 team as a reserve driver for 2020, with his backer PKN Orlen coming on board as a "co-title sponsor".
In 2019, Kubica made his return to the F1 grid with Williams following a long absence triggered by his life-threatening rally crash.
The 35-year-old scored Williams's sole point in what proved to be a miserable season for the team, with Nicholas Latifi taking his place for 2020.
Kubica was linked with a simulator role at Haas and Racing Point, but will join Alfa instead.
His new role was revealed at the same time as "a multi-year partnership" between the team and Polish oil company PKN Orlen was announced, which will mean the squad competes as 'Alfa Romeo Racing ORLEN' this year.
"I am really happy to be starting this new chapter in my career as I join Alfa Romeo Racing ORLEN," said Kubica, who raced for the team when it was known as BMW Sauber from 2006 to '09.
"This team holds a special place in my heart and I am pleased to see some faces still here from my years in Hinwil.
"Time and circumstances are obviously different, but I am convinced that I will find the same determination and hunger to succeed.
"I am looking forward to helping Alfa Romeo Racing ORLEN make the next step forward."
During Kubica's time with BMW Sauber, he won the 2008 Canadian Grand Prix and finished in a personal best fourth place in the that year's drivers' championship.
Alfa has retained an unchanged race line-up of Kimi Raikkonen and Antonio Giovinazzi for 2020, and has confirmed that its next F1 challenger will be called the 'C39'.
"We are also delighted to welcome Robert back home and we cannot wait to start working with him," said team principal Frederic Vasseur.
"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."