The white-and-red scheme, reflecting Alfa Romeo's colours, marks a move away from the predominantly blue livery which Sauber has run since 2015.
That deal, marking the return of the historic Alfa Romeo name to Formula One after a more than 30-year absence, was announced earlier in the week.
This season the 20-year-old from Monaco has tested with both Ferrari and Sauber, and enjoyed another four F1 practice outings with the latter, who will be known as the Alfa Romeo Sauber F1 Team for 2018.
Meanwhile Ericsson, who failed to score a single point in 2017, takes the other seat ahead of Antonio Giovinazzi, who competed in the Australia Grand Prix and the Chinese Grand Prix as Pascal Wehrlein recovered from an injury sustained at the Race of Champions. He was speaking in Milan at an event marking the launch of Sauber's new partnership with Alfa Romeo.
"Formula One is the natural reference point for a marque like this", he said.
"The motor we use will be the same one Ferrari use", Marchionne said. "I think the guns are loaded in a different way".
Sauber finished last in the constructors' championship for the first time in their history in 2017.
"I think obviously we're starting from quite far behind because we had a hard season, but I think we have the potential to take a good step forward".
The news was announced Saturday as the team's Formula One auto was also unveiled with it's slick red and white colouring with a prominent Alfa Romeo logo.