Hulkenberg contested two grands prix for the team last year, in place of Sergio Perez in the 70th Anniversary Grand Prix and Lance Stroll at the Eifel Grand Prix, while a start in the British Grand Prix did not eventuate due to a mechanical problem.
“First of all, it's great to get this deal signed up with plenty of notice – last year, I didn't have quite as much time to prepare before jumping in the car,” said Hulkenberg, who was initially called up last year when Perez contracted COVID-19.
“I'm really pleased to once again work with this team – with whom I have driven many times during my career.
“Obviously, I'm hoping that Sebastian and Lance enjoy uninterrupted seasons this year, but the team knows it can rely on me to step in and do an excellent job, and I'm fully prepared to take on that challenge.
“It will also be interesting to help develop the team through the season, and I'm really looking forward to pulling great lap times out of my arm sleeve.”
Team principal Otmar Szafnauer said, “We're delighted to be able to welcome Nico back to the team in an official capacity, as reserve and development driver for Aston Martin Cognizant Formula One Team.
“In these difficult times, the requirement for a capable and experienced reserve driver is especially important.
“Nico proved last year that he could jump in the car and perform superbly at a moment's notice; now, with additional scope for preparation and integration, we know that we can rely on Nico to do an excellent job.”
Hulkenberg raced full-time for Force India, which morphed into Racing Point and is now known as Aston Martin, from 2012 to 2016.
Round 2 of the 2021 season is the Emilia Romagna Grand Prix, on April 16-18.