James Calado will take part in FP1 at the Italian GP after being handed the reserve and test driver duties at Force India.
The 24-year-old impressed during the Young Driver Test at Silverstone in July and Force India have decided to hand him the back-up role to Paul di Resta and Adrian Sutil.
His first bit of official Formula One action will be this weekend when he takes part in the first session at Monza.
"I'm pleased to confirm that we've signed James as our third driver," team principal Vijay Mallya said.
"We worked with him during the Silverstone test and he impressed everyone with his speed and consistency. We've always tried to support young drivers and this is a great opportunity for James to gain some valuable experience of driving during Formula One race events."
He added: "James will take part in the opening free practice session on Friday. He will also run in practice at several other races this year. It's always useful to get another driver's feedback on the car and it will help us evaluate James."
Calado has driven in the Formula Renault 2.0 UK, Eurocup Formula Renault 2.0, British Formula Three and GP3 Series over the past few years, but he has been competing in the GP2 Series with ART Grand Prix since 2012.
He finished fifth last year with one victory and is once again P5 in the standings this year with two wins under his belt.