Smith Jr. was born in New Orleans, Louisiana on August 9, 1998. Shortly after being born, he moved to Arizona where he spent the first 14 years of his life. Smith Jr. moved back to New Orleans at age 14 and attended Brother Martin High School in New Orleans, Louisiana, where he played high school football. As a senior, he had 31 receptions for 558 yards and four touchdowns. He originally committed to Texas A&M University to play college football, but changed to the University of Alabama.
After not recording a reception as a true freshman at Alabama in 2016, Smith Jr, had 14 receptions for 128 yards and three touchdowns over 14 games as a sophomore in 2017. He returned to Alabama as a starter in 2018. On January 11, 2019, Smith announced that he would declare for the 2019 NFL Draft.
Smith Jr. was drafted by the Minnesota Vikings in the second round with the 50th overall pick in the 2019 NFL Draft. Smith made his NFL debut in Week 1 against the Atlanta Falcons. He recorded his first reception in the next game against the Green Bay Packers. He recorded a season-high and team-leading 60 receiving yards on three receptions against the Oakland Raiders in the following game. He scored his first professional touchdown in Week 11 against the Denver Broncos on a 10-yard reception from Kirk Cousins. Overall, as a rookie, he appeared in all 16 games and started six. He recorded 36 receptions for 311 receiving yards and two receiving touchdowns. In Week 9, against the Detroit Lions, Smith had two receiving touchdowns in the same game for his first multi-touchdown game as a professional. In Week 16 against the New Orleans Saints on Christmas Day, Smith recorded 6 catches for 53 yards and 2 touchdowns during the 52–33 loss.
Like Father Like son. Smith's father, Irv, was the 20th overall pick of the 1993 NFL Draft by New Orleans. The older Irv totaled 183 receptions for 1,788 yards and 15 scores in seven NFL seasons. He spent 1993-97 with the Saints before playing one season with San Francisco and closing his career in Cleveland.
Smith was a four-star recruit out of Brother Martin High School, an all-male, Catholic, college preparatory school in New Orleans. He was a 2015 5A All-State Honorable Mention selection and chose Alabama over Texas and Texas A&M.