The 28-year-old, who can play full-back or on the wing, will join the club until the end of the season after he was released by Perpignan and registered within the deadline period for the current campaign.
Director of Rugby Philippe St Andre said: "Julien is a high level international player with 11 caps and will be an exciting addition to our back division until the end of the season."
Laharrague's initial three-month deal also gives the club the option to extend the contract at the end of the season.
St Andre added: "We have two massive games against Worcester and Northampton, followed by the EDF Energy Cup semi-final in Cardiff.
"Julien is not currently in the French squad and will be able to help us in this demanding period of the season."
Laharrague will arrive on Monday and could make his debut against Worcester at Edgeley Park next Friday.
There was more good news for Sale and England earlier when captain Jason Robinson was told he will not need surgery on the neck injury which kept him out of England's record RBS 6 Nations Championship defeat to Ireland last weekend.
Robinson missed Saturday's 43-13 defeat at Croke Park but saw a specialist last night who advised him to rest for a few days to let the neck pain settle down, meaning he could be in contention for England's game with France at Twickenham on March 11.
"The good news is that the problem should not need any corrective surgery and, with the correct rest and rehab, Jason should be back playing very soon," said Sale club doctor Dave Jones.
Magnus Lund, Robinson's team-mate for club and country, is also currently recovering from a head injury picked up at Croke Park.
Jones feels Sunday's Premiership trip to Saracens will come too soon for the flanker, but the following weekend's Six Nations clash with France may mark his return.
"Magnus will not play again until he has taken and passed the necessary tests," Jones said.
"It is very doubtful he will play this weekend [at Saracens on Sunday] but we are hopeful he will be fit next week."