The former England central defender has been a free agent since quitting League Two Notts County in September, just one match into a five-year contract.
"We gave him the opportunity to re-launch his career and for us it is a good help to the end of the season and for him it is a good opportunity to show that he still can play in the Premier League," Wenger told reporters on Friday.
Campbell, who won two league titles and three FA Cups in a previous spell with Arsenal and played in two World Cups, has not featured in the top flight since leaving Portsmouth when his contract expired last July.
Wenger believes the defender, who last played for the London club in the 2006 Champions League final, still has plenty to offer after training with the club in recent weeks.
"He brings experience, good advice and he's physically worked very hard," Wenger said.
"I think he showed he was dedicated and motivated and looked happy to be back here. Many players are always happy to be back at Arsenal."
Campbell will not feature in Arsenal's match at Bolton Wanderers on Sunday, having played just 45 minutes in a reserve match this week, but could provide useful cover to William Gallas and Thomas Vermaelen in the months ahead.
"It just depends on his performances and overall at the moment Gallas and Vermaelen are the two starters in the team," Wenger said.
Campbell's surprise move to County, where former England manager Sven-Goran Eriksson was director of football, sparked huge interest but he played just once, in a 2-1 defeat by Morecambe, before tearing up his contract.
