Alfa Romeo will return to the sport after an absence of 30 years as Sauber's title sponsor, with the Swiss team strengthening its Ferrari ties, having cancelled its planned Honda partnership.
Charles Leclerc, 20, will make his Formula One debut as a full-time driver in the 2018 season driving for Sauber.
Leclerc is a current member of the Ferrari Driver Academy, and he is widely considered one of the future stars of Formula One.
Leclerc has risen rapidly through the single-seater ranks, winning the GP3 title past year before his F1 championship triumph this season.
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. The Italian vehicle manufacturer is making a return to the sport after 30-years to sponsor the team.
The covers were then pulled off a showcar, revealing a red and white livery, with a large Alfa Romeo logo on the engine cover.
Formula One chairman Chase Carey and former Ferrari boss Jean Todt, president of the governing FIA, both attended the presentation.
Ferrari's late founder Enzo also started out racing and managing a team for Alfa Romeo, before setting up on his own in the late 1930s.