Chark had offers from schools such as Memphis, Oklahoma State, Texas A&M, among others. He chose to commit to Louisiana State University (LSU) to play college football. Chark played at LSU from 2014 to 2017 under head coaches Les Miles and Ed Orgeron. After not recording a reception his first two years, he had 26 for 466 yards and three touchdowns as a junior in 2016. As a senior in 2017, he had 40 receptions for 874 yards and three touchdowns. Known for his straight-ahead speed, Chark earned the nickname “The Flash” during his time at LSU. He wore number 7 at LSU.
On December 18, 2017, it was announced that Chark had accepted his invitation to play in the 2018 Senior Bowl. On January 27, 2018, Chark played in the 2018 Reese's Senior Bowl and made two tackles and caught five passes for 160 receiving yards and two touchdowns as part of Houston Texans head coach Bill O'Brien's South team that defeated the North 45–16. He led both teams in receiving yards and earned the Senior Bowl's co-MVP award. Chark's Senior Bowl performance immediately garnered him recognition as a top wide receiver prospect in the upcoming draft and he was widely praised among analysts, including Charles Davis and James Jones.
He attended the NFL Scouting Combine in Indianapolis and completed all of the combine and positional drills. His draft stock continued to rise after he tied for fourth among all players in the 40-yard dash, tied for ninth in the vertical jump, and tied for 13th in the broad jump. Chark also attended a private workout for the Dallas Cowboys and pre-draft visits with the Buffalo Bills and Denver Broncos. At the conclusion of the pre-draft process, Chark was projected to be a second round pick by NFL draft experts and scouts. He was ranked the fifth best wide receiver prospect in the draft by DraftScout.com, was ranked the sixth best wide receiver by Scouts Inc., and was ranked tenth best wide receiver by Sports Illustrated.
On May 25, 2018, the Jacksonville Jaguars signed Chark to a four-year, $4.44 million contract that includes a signing bonus of $1.31 million. In the Jaguars' Week 2 victory over the New England Patriots, Chark recorded his first professional reception, which went for 13 yards. However, he did lose the ball on a fumble on the same play.