Arsenal are sixth in the Premier League and have only won one of their five games since the turn of the year.
They have not won a trophy since 2005 but Pires, who made 285 appearances and won six trophies with the club before leaving to join Villarreal, believes Wenger will get them back into the top four come May.
The 39-year-old said: "For me, I always believe in Wenger.
"Everyone knows the task is to qualify for the Champions League again next season. The team has been too inconsistent this season to do much more.
"Against Manchester City recently it was very difficult and against Swansea a few days later Arsenal were better but there have been too many games where they are up and down."
Pires also defended striker Olivier Giroud, who has scored nine goals in 30 appearances since joining from Montpellier in the summer.
He added: "The people need to give Olivier time. I know he is a good player.
"It is very difficult to adapt from French football and everyone needs time, even Thierry [Henry] did in the first half of his first season at the club.
"I would tell supporters to relax, Olivier will score goals."