[1] His maternal uncle, Mike Gallego, played in Major League Baseball (MLB) for the Oakland Athletics.

As a shortstop in Little League Baseball, Barnes' nickname was "Hoover", given for his ability to field ground balls.

[2] He attended Riverside Polytechnic High School, playing on the same baseball team as future Houston Astros outfielder Jake Marisnick.

[3] He received four varsity letters from Riverside Poly, and served as team captain his senior year.

[2] After graduating from Riverside Poly, Barnes attended Arizona State University to play college baseball.

After catchers Xorge Carrillo and Andrew Pollak both suffered injuries during Barnes' sophomore season, he was called behind the plate.

[7] He started in 48 games, 43 of which were behind the plate, and earned registered a .985 fielding percentage in his first season as a full-time catcher.

[5] Barnes was given an opportunity to return to the infield for his junior season, but he elected to remain the team's catcher.

[11] On December 10, 2014, Barnes was traded to the Los Angeles Dodgers, along with Chris Hatcher, Andrew Heaney, and Enrique Hernández, in exchange for Dan Haren, Dee Gordon, Miguel Rojas and cash.

[16] He returned to Oklahoma City after his short time on the Dodgers roster and was named as a starter on the Pacific Coast League team for the mid-season Triple-A All-Star game.

[24] He gradually saw more playing time, moving into a platoon role with Grandal for most of the season before taking over as the starter in the playoffs.

[21] In the 2017 NLDS Barnes had four hits in eight at-bats with a home run and a double in the Dodgers' three-game sweep of the Arizona Diamondbacks.

[26] He ended up being the backup to Yasmani Grandal, taking over the catching role more in the postseason when Grandal allowed two passed balls and made two errors in game 1 of the NLCS and another passed ball in game 3, resulting in Dodgers fans booing him and begging for Barnes to catch.

[29] In 2019, Barnes was named the Opening Day starting catcher after Grandal signed with the Milwaukee Brewers.

However, he got off to a slow start and on July 26 he was sent down to Oklahoma City to make room for rookie catcher Will Smith to take over the everyday catching duties.

On February 15, 2021, Barnes signed a new two-year, $4.3 million, contract with the Dodgers, to avoid salary arbitration.

[21] While Barnes was active for the entire postseason in 2024, he only made one appearance, as a defensive replacement in the NLCS, as the Dodgers won the 2024 World Series title.