In February 2021, Kelenic stated that the Mariners had kept him in the minor leagues during the 2020 season because he had refused to sign an extension. His comments occurred after a video of Mariners CEO Kevin Mather speaking to a rotary club was posted online. Mather indicated that Kelenic and fellow Mariners prospect Logan Gilbert would start the 2021 season in the minor leagues, keeping them under team control for an extra year before free agency.[23] After the comments became public, Kelenic said that the Mariners had offered him a contract extension and had told him multiple times that he would have appeared with the major league team in 2020 had he signed it. Instead, Kelenic spent the 2020 season at the team's alternate training site. In response, Mariners general managerJerry Dipoto said that Kelenic was not yet ready to play on the major league team.[24][25] Despite impressing during spring training, with two home runs and a 1.256 OPS in nine games, Kelenic was assigned to the Tacoma Rainiers of the Triple-AWest League to begin the 2021 season.[26][27]
On May 13, 2021, Kelenic was added to the 40-man roster and promoted to the major leagues for the first time.[28] He made his debut that day as the starting left fielder against the Cleveland Indians, going hitless in four at-bats. The next day, on May 14, Kelenic recorded his first MLB hit, a two-run home run in the bottom of the third inning for an estimated distance of 403 feet.[29] On June 7, 2021, amid a 0-39 slump, he was sent down to Triple–A.[30] In June 2021, Kelenic was selected to play in the All-Star Futures Game.[31] Kelenic was called back up to the major leagues after the All-Star break and stayed on the roster for the remainder of the season, contributing to the Mariners' ultimately unsuccessful late-season playoff push.[32][33] Kelenic finished the 2021 season batting .181/.265/.350 with 14 home runs and 43 RBIs in 93 games.[34]
2022
Prior to the 2022 season, due to his performance during the tail end of the Mariners' 2021 season and his previous high prospect status, Kelenic was viewed as a candidate for a breakout season.[35] Kelenic began the 2022 season with the Mariners. In May 2022, he was optioned to Tacoma after hitting .140/.219/.291 over 30 games.[36] After being sent down to the minors, in 54 games for Tacoma, Kelenic slashed .288/.363/.540 with an OPS of .903.[37] He was then called back up to the majors on July 31, replacing Julio Rodríguez, who had been placed on the injured list after getting hit by a pitch.[38] During his short 10-game stint with the major league squad, he had just two hits in 27 plate appearances before being optioned once again to Tacoma.[39]
Kelenic was once again called up in late September, again hitting well[clarification needed] within the final month of the regular season as well as during the postseason, the Mariners' first since 2001.[40][41] At the end of the 2022 season, Kelenic had a career batting average of .168, second to John Vukovich for lowest in history for batters with more than 550 plate appearances.[42]
2023
During the offseason, Kelenic worked on adjusting his approach at the plate to one that would be more suitable for hitting major-league pitching, especially towards breaking balls, which he greatly struggled hitting while he was in the major leagues.[43][44] Before the 2023 season, Kelenic was again viewed as a breakout candidate because of his performance after his final call-up, as well as the ban on the infield shift that was introduced in 2023.
In spring training, Kelenic flourished, slashing .353/.389/.706 with four home runs in 54 plate appearances. Kelenic began the season on the Opening Day roster, with the intent of platooning in left field with the newly-acquired A. J. Pollock.[45] Kelenic continued his spring training success into the major league season, hitting well enough to earn starts against left-handed pitchers and became the everyday left fielder.[46] On April 12, 2023, Kelenic hit a 482-foot home run that landed in the second tier of the center field bleachers at Wrigley Field, the longest regular-season home run recorded at Wrigley and the longest by a Mariner during the Statcast era (since 2015).[47]
On July 20, Kelenic broke his foot after kicking a water cooler during a game against the Minnesota Twins.[48] He was activated off of the injured list on September 11.[49]
Kelenic finished his 2023 season batting .253/.327/.419, with 11 home runs and 49 runs batted in.
Atlanta Braves
On December 3, 2023, the Mariners traded Kelenic, Marco Gonzales, and Evan White to the Atlanta Braves for Jackson Kowar and Cole Phillips.[50] Atlanta initially announced that Kelenic would be their starting left fielder, but after a brutal Spring Training (Kelenic slashed .143/.200/.232), Adam Duvall was acquired to platoon with Kelenic in left. However, after Duvall struggled and injuries plagued the Braves' outfield, Kelenic became the starting everyday center fielder, and took the leadoff spot in the lineup.