Robert Kubica's dream of an F1 comeback this year will only be partially fulfilled, with the Polish driver handed a reserve and development role with Williams in 2018.
The 32-year-old ramped up his F1 testing in preparation last year after a six-year hiatus from the sport following his rally accident in early 2011.
Kubica's endeavor culminated with a post-season test with Williams in Abu Dhabi last November, but the team ultimately chose to include Sergey Sirotkin in its 2018 driver line-up.
"I’m extremely happy to be joining the Williams team as its official Reserve and Development Driver this season," said Kubica.
"I feel in the best physical shape that I have ever been, but it has taken a lot of work to get to where I am now, so I’d like to thank Williams for the opportunities they have given me so far, and for putting their faith in me with this appointment.
"I have enjoyed being back in the Formula One paddock over these past few months, and I now look forward to working with the Williams technical team, both at the factory and at the track, to really help push forward the development of the FW41 and to make a real difference to their 2018 campaign."
In his development role, Kubica is expected to take part in pre-season testing, a yet-to-be-determined Friday practice sessions and extensive simulator work.
"Having driven both the FW36 and the FW40, I’m looking forward to seeing how the FW41 measures up on track and working with the team to ensure we can maximise the performance of the car.
"My ultimate goal remains to race again in Formula 1 and this is another important step in that direction: I cannot wait to get started."
Williams deputy team principal Claire Williams:
"I am delighted to announce that Robert will be joining Williams as our Reserve and Development Driver for the 2018 season.
"All of us at Williams have been immensely impressed at what he has achieved, and it is a great credit to his strength of character and commitment to return to Formula One.
"We are excited to be continuing our relationship with Robert and look forward to working with him this coming season."