The 27-year-old failed to make a senior appearance for Benfica after joining from the Hoops in 2015 and has failed to even turn out for the reserve side since January 2016.
Taarabt was dropped by the Portuguese club after being caught partying the night before a match, despite having three-and-a-half years still to run on his contract.
"Genoa was my destiny, I played twice at Marassi and I scored two goals," Taarabt said of his loan move.
"I missed Italy and now I feel well physically even though it's been a year and a half since I played [first-team football]. I want to repay Genoa for believing in me."
Taarabt featured 157 times in the Premier League and Championship during his six years with QPR.