The 34-year-old former Gunners captain will go straight into the squad for Monday night’s FA Cup third-round clash against Leeds at the start of a six-and-a-half-week spell which will take in games against Manchester United, AC Milan and possibly even the visit of Tottenham on February 26.
Henry became Arsenal’s record goalscorer during eight seasons with the north-London club before joining Barcelona in 2007.
Wenger believes his return can only be good for all involved.
He said: “You cannot take away from people what they have done, and what he has delivered will stay forever.”
“Thierry is a world-class player and even at this club a player of that dimension is always very difficult to find, especially at this period of the season. He can just add something more to the team.
“Who would turn down a player of his quality?
“We have a good spirit in the side and he will add something more, experience-wise, and on the nervy side as well, when we are under pressure.
“That is a good addition because he knows the club, he knows the league, and it is only positive.”
Wenger is in no doubt Henry still has the quality to compete at the highest level, the striker having trained at his old club since the end of the Major League Soccer season.
“When you are a young striker you are more focused on yourself and today, what he can give to others is of a higher level than he could do five or six years ago.
Wenger added: “We want him to perform. I want him to help the team and do well.
“I don’t even have to say a word because he will want to do that himself.”
Henry admitted he never expected to return to Arsenal, but when the opportunity presented itself he could not turn it down.
The France World Cup winner said: “It did happen pretty fast but when it comes down to Arsenal it is pretty hard for me to say no.
He told the club’s official website: “When it comes to Arsenal my heart will always do the talking. Once I knew the plan behind it I was okay with it. I am not coming here to be a hero or prove anything. I am just coming here to help. People have to understand that.”
Henry continued: “I want to send a message to the fans of New York Red Bulls as well. I always said I would not play in Europe again.
“But it is hard for me when it comes to Arsenal. I am not coming here for the whole season, I will be back and I want to win the MLS Cup with the Red Bulls. I hope it is a win-win situation where I can help Arsenal and come back fit for the MLS season.”
Arsenal’s Barclays Premier League ambitions took a knock with defeat at Fulham, where they lost 2-1 in stoppage time after having defender Johan Djourou sent off when they were in front.
Wenger expects a response from his injury-hit squad. He said: “The schedule was very tough for us and I feel as well we were really unlucky over the Christmas period.
“I cannot fault the players’ attitude or spirit and that’s why I’m still optimistic and I think in the end the quality of that spirit will come through.
Meanwhile Arsenal’s defensive crisis has deepened ahead of the visit of Leeds.
Johan Djourou is suspended, while Kieran Gibbs, Thomas Vermaelen, Bacary Sagna, Carl Jenkinson and Andre Santos are all unavailable through injury.
Wenger admits he will have to bring in some cover during January, with former England full-back Wayne Bridge — now surplus to requirements at Manchester City — a potential acquisition.