On July 12, Gurriel was promoted to the New Hampshire Fisher Cats of the Double-A Eastern League after appearing in 18 games for Dunedin. In total, Gurriel played in 64 games in 2017 and hit .229 with five home runs and 36 RBI. He played for the Peoria Javelinas of the Arizona Fall League (AFL) during the offseason. Gurriel began the 2018 season with New Hampshire. He batted .347 in 12 games, and was promoted to the major leagues on April 20. In his debut that night, Gurriel recorded two singles and three RBI. On April 28, Gurriel hit his first career home run, against Bartolo Colón of the Texas Rangers. On July 27, Gurriel recorded his first multi-home run game by hitting two home runs in a 10-5 win over the Chicago White Sox. By collecting a pair of singles in Toronto's game against the White Sox the following night, Gurriel became the first rookie in baseball's modern era to have 10 consecutive multi-hit games. The last rookie to accomplish this feat was Shoeless Joe Jackson in 1911. On July 29, Gurriel broke Jackson's rookie record with his 11th consecutive multi-hit game. Jackson also set the overall AL record with an 11-game multi-hit streak in 1912. Simultaneous with breaking Jackson's 1911 rookie record, Gurriel also tied Jackson's all-time AL record. However, on his third hit of the game on July 29, Gurriel was injured, and was subsequently put on the disabled list. On September 25, Gurriel was shut down for the rest of the season with a sore left hamstring. After starting the 2019 season hitting .175 in 13 games and struggling with throws from second base, the Blue Jays optioned Gurriel to the Buffalo Bisons of the Class AAA International League. At Buffalo, Gurriel began playing as an outfielder. On defense in 2019 with Toronto he led all major league left fielders in assists, with 9. On offense, he finished hitting .277 with 20 home runs in 84 games. His brother, Yuli Gurriel, also played in Cuba before defecting, and later signed with the Houston Astros. His family lives in Miami, Florida. Lourdes and his brother made Major League Baseball history on September 21, 2018 when each hit two home runs, becoming the first brothers to have multi-homer performances on the same day. Lourdes Gurriel Jr. is the son of Lourdes Gourriel.