Vergne, who raced for Toro Rosso for three seasons between 2012 and 2014, will work on car development in the Ferrari simulator, operating alongside the team's newly appointed test and third driver Esteban Gutierrez. Meanwhile, previous test driver Pedro de la Rosa will leave the team at the end of the year.
"On behalf of the entire team, I welcome Jean-Eric, who I'm sure will make an important contribution to our development work in the simulator," said Ferrari team principal Maurizio Arrivabene.
"He will fit in to a programme aimed at improving important areas, invigorating and strengthening an already strong and capable group of professionals."
Frenchman Vergne, 24, added: "I feel very honoured to be joining the Ferrari family and becoming a part of the most prestigious team in the history of Formula One.
"The objective is a unanimous one and that is to help the Scuderia get back to the top step of the podium. Having had two years working in the simulator for a top F1 team and three years racing with Toro Rosso, my experience will add to the great efforts that are currently being made in order to get the team back to its winning ways.
"I look forward to fulfilling my dream in becoming a member of Scuderia Ferrari and having the tifosi behind me every step of the way."
As well as Vergne and Gutierrez, Ferrari can also call upon Marc Gene and Davide Rigon as test drivers.