Leclerc, 20, will line up alongside Swedish driver Marcus Ericsson. 

The Monegasque replaces Pascal Wehrlein, with Antonio Giovanazzi missing out on a seat - instead settling for the third driver role.  

The announcement came as Sauber revealed a concept Alfa Romeo livery following their partnership with the Italian car manufacturer. 

The deal will see Sauber forge a closer relationship with the Scuderia Ferrari team. 

Sergio Marchionne, the chairman of both Ferrari and FIAT-owned Alfa, officially launched the car brand's return after a 30-year absence.

Leclerc joins Sauber after having tested for Ferrari the last two years. 

He is one of the most highly-rated young drivers in motorsport, having won the 2017 FIA Formula 2 Championship, and was also the GP3 Series champion in 2016.