The Wildcats head coach, who was shortlisted for the England job two years ago, takes over from Frenchman Aurelien Cologni in the run-up to the 2013 World Cup.
Agar, who was unveiled on Monday morning at a press conference in Toulouse, will retain his full-time job with his Super League club and work part-time with the French.
"I'm very proud and very honoured to be offered the position to be a head coach of a national team," he said.
He added: "It was a little bit of a surprise. I got the phone call about a month ago and it was very kind of the club as both (Wakefield chairman) Andrew (Glover) and (chief executive) James (Elston) gave me their blessing to go and meet the French people to look at the levels of commitment and when I'd be required to be over there.
"I think it's a great opportunity and an opportunity I want to take and be very proud to take. I think it's a great time to be involved with them."
Elston said: "It's a fantastic opportunity for Richard to work with some top-class players and test himself against some of the best coaches in the world later this year.
"He takes the role with our blessing and knowing how hard he works, I'm certain he'll make a success of taking the French side into a tournament that will be a tremendous showcase for the sport.
"It won't impact his work with the club and we see the opportunity for Richard to develop as a positive not only for him, but the extra experience he will bring back can only be of benefit to our players and coaching staff."
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