[12] In 25 games (23 starts) between the three clubs, he was 15–4 with a 1.41 ERA and a 1.02 WHIP[13] and he was named the USA Today Minor League Pitcher of the Year.

[18] He picked up his first career major league win on June 27, when he allowed four runs in 5+1⁄3 innings against the Boston Red Sox.

[23] On June 3, he tied an AL record by striking out the first seven batters he faced in a game against the Seattle Mariners at Safeco Field.

[24] At the time of the All-Star team announcement, Snell was 12–4 with a 2.09 ERA, the lowest of all qualified pitchers in the American League.

[33] On September 23, he won his 21st game, setting a franchise record after pitching 62⁄3 scoreless innings with 11 strikeouts against the Toronto Blue Jays.

[36] His 1.89 ERA was the lowest in the American League since Pedro Martinez posted a 1.74 in 2000, and the third-lowest in the AL since the designated hitter was introduced in 1973.

[40][41] On November 14, Snell won the American League Cy Young Award, topping runner-up Justin Verlander by 15 points (169–154) and receiving 17 of 30 first-place votes.

[38] On March 21, 2019, Snell agreed to a five-year contract worth $50 million to keep him with the Rays through the 2023 season; it was the largest deal given to a major league pitcher before they reached salary arbitration.

[45] On April 16, Snell he was placed on the injured list after breaking a toe on his right foot while moving furniture in his bathroom, and missed two starts.

[46] On July 25, it was announced that he would undergo arthroscopic surgery to remove loose bodies from his left elbow.

[49] Before the start of the delayed MLB season, Snell caused some controversy when he said that he was more concerned about his pay than health when it came to decisions to return to play during the COVID-19 pandemic.

[53] Snell started the first game of the postseason against the Toronto Blue Jays in the Wild Card Series, taking a no-hitter into the 6th inning as the Rays won.

[55] In Game 2 of the 2020 World Series against the Los Angeles Dodgers, Snell allowed two runs and struck out nine batters in 4+2⁄3 innings.

The Dodgers then scored two runs that inning and would go on to win the game 3–1 and the World Series, resulting in criticism by fans and baseball media.

[59] On December 29, 2020, the Rays traded Snell to the San Diego Padres in exchange for prospects Luis Patiño, Blake Hunt, and Cole Wilcox, along with catcher Francisco Mejía.

[61] Snell initially had trouble going deep into games, not completing six innings until his ninth start of the year.

[64] Snell finished strong, posting a 1.83 ERA in his final eight starts of the year,[65] including seven innings of no-hit ball against the Diamondbacks on August 31.

[67] Snell's preparations for the 2022 season were interrupted by the lockout, and he was behind the other starting pitchers in building innings in spring training.

[68] In his first scheduled start of the regular season, Snell again felt adductor tightness while warming up in the bullpen and he did not pitch in the game.

[70] With Snell's return, the Padres opted to go with a 6-man rotation to keep MacKenzie Gore in the starting line-up and lower stress on arms.

[75] On March 19, 2024, Snell signed a two-year, $62 million contract with the San Francisco Giants that contained an opt-out after the first year.

[76] He made his debut on April 8, 2024, against the Washington Nationals, pitching in three innings and allowing three earned runs, taking the loss.

[78][79] On July 27 at Oracle Park, against the Colorado Rockies, Snell struck out a career-high 15 batters over six scoreless innings.