He played in Major League Baseball (MLB) for the Philadelphia Phillies, Pittsburgh Pirates, Seattle Mariners, Texas Rangers, and San Francisco Giants.

He played college baseball for the University of California, Berkeley, and was selected by the Phillies in the second round of the 2013 MLB draft.

[2] During his childhood, he followed his father Mike, a minor league catcher, across the country, visiting 38 states by the time he was five years old and living in at least six of them.

[3] Mike, who never made the major leagues, was a right-handed hitter, which he attributes as part of the reason he never broke in at the big-league level.

[4] Andrew started hitting left-handed—and eventually as a switch hitter—at the suggestion of his mother, who wanted her son to avoid her husband's fate.

[10] He made his professional debut with the Williamsport Crosscutters where he posted a .253 batting average with 20 doubles (tied for the league lead), four home runs, and 23 RBIs in 62 games.

[11][12] He spent 2014 with both the Lakewood BlueClaws and Clearwater Threshers,[13] hitting a combined .260/.324/.385 with six home runs and 32 RBIs in 98 games and was named an MiLB.com Organization All Star.

[14] Knapp started 2015 with Clearwater where he was a mid-season FSL All Star, and was promoted to the Reading Fightin Phils during the season.

[17] Knapp did, however, take strides defensively, which at the time was viewed as an area of relative weakness that he would need to improve to have a chance at the major league level.

A great thing about Knappy is he cares a lot more about the pitch calling and defensive catching than he does hitting.

On July 1, 2018, Knapp hit the team’s first walk-off home run since 2016, a 13th inning blast against the Washington Nationals.

[2] Despite his paltry overall hitting performance—a .198 batting average with four home runs and 15 RBIs in 187 at bats—the team began to value Knapp's defensive and game management skills along with his ability to get on base.

[28][29] During the offseason prior to the Phillies' 2019 campaign, they acquired J. T. Realmuto in exchange for a package of prospects that included Alfaro, again opening a clear path for Knapp to start the season as the team's backup catcher.

[2] Although he continued to struggle offensively, Phillies' management expressed comfort with keeping Knapp as Realmuto's backup moving forward.

[32] The Phillies' catching situation remained unchanged entering spring training in 2020, with Knapp projected to serve as Realmuto's backup, and that eventually was the case once the season began in July after a delay due to the COVID-19 pandemic.

[36] Knapp ultimately played 33 of 60 games during the shortened season, hitting a career-best .278 with two home runs and 15 RBIs.

[43] On April 5, 2022, the same day as his release from the Reds, Knapp signed a major league contract with the Pittsburgh Pirates to serve as the team's backup catcher.

On August 31, Knapp's contract was selected from the Triple-A Sacramento River Cats, after batting .312/.373/.634 with the club in 102 plate appearances.

On August 23, 2024, Knapp signed a one-year major league contract with the San Francisco Giants.

[20][62] Over the course of his first several seasons at the major league level, Knapp often started on days when Zach Eflin pitched.