The 34-year-old winger, who plays for Al Ahli - the reigning Asian champions - scored once and assisted twice in Algeria’s 3-0 win over Somalia in the penultimate round of African qualifying, securing top spot in Group G and a place at next year's finals in the United States, Canada and Mexico.
"This will be my last World Cup. I'm not Ronaldo," Mahrez told Algerian media.
"I'll give everything I have to represent Algeria in the best possible way."
Mahrez, who turns 35 in February, now has 33 goals in 106 international appearances. He praised his teammates, coach, and fans for their support, saying the team "dominated from start to finish" and that the focus now shifts to the Africa Cup of Nations.
"I thank God for this important win," he said. "I'm happy to have helped with two assists, but the most important thing is that we've officially qualified."
Algeria have now qualified for the World Cup for the fifth time following appearances in 1982, 1986, 2010 and 2014. Their best performance came in 2014 in Brazil, where they reached the round of 16 for the first time before falling to eventual champions Germany in extra time.