Lotus said that the aim of the pre-arranged move is to give Indian Chandhok a chance to prove himself.
Trulli, known for being an excellent qualifier in the past, has been struggling this season, being out-qualified by Finnish teammate Heikki Kovalainen in eight of the nine races.
"It's great that the team is true to its word of helping develop young talent, particularly from parts of the world where it is even harder to break through into the top rung of motorsport, so I'll be there to give him guidance and assistance, in and out of the car," said the Italian veteran.
Chandhok, 27, who has not raced in F1 since last year's British GP, said: "Ever since I first joined the team I have been looking forward to this opportunity and I am determined to do my best to repay their faith in me."
Trulli will return to action at the next round of the World Championship in Hungary.