A veteran of 162 appearances in Serie A, the 25-year-old midfielder has signed a two-year loan with an option for a third season.
"We're very happy to welcome Saphir with our club," said Impact president Joey Saputo, who also serves as a co-owner at Bologna. "He's a very competitive player who has played over 100 games with Bologna FC since 2012. This signing will help the team to reach his goals."
Taider is expected to fill the void in central midfield left by Blerim Dzemaili, who returned to Bologna this offseason after spending the 2017 MLS campaign on loan to Montreal.
"It's an excellent signing for our club because Saphir is both young and has a lot of experience on the European stage," Impact coach Remi Garde said. "His career thus far in some of Serie A's biggest clubs and with the Algerian national team makes him a very important player who can help the Impact win trophies in the seasons to come.
"After explaining the project being put in place here in Montreal, to my great satisfaction, he chose to accept this challenge and to invest himself fully. His European track record and his position in midfield will give him many responsibilities. I am convinced that he has all the capacities to become one of the top players in MLS."