Kaczmarski graduated from Prairie Ridge High School in Crystal Lake, Illinois in 2010.

[2] As a senior in 2015, he played in 46 games and hit five home runs with 57 RBIs[3] and led the nation with a .465 batting average.

After signing, Kaczmarski made his professional debut that same year with the Kingsport Mets and spent the remainder of the season there, batting .355 with four home runs and 34 RBIs in 64 games.

In 2016, he played for both the Columbia Fireflies and St. Lucie Mets, slashing a combined .280/.360/.413 with two home runs and 46 RBIs in 111 total games between both teams, and in 2017, he played for the Binghamton Mets where he hit .274 with five home runs, 52 RBIs, and 15 stolen bases in 128 games.

[9] Kaczmarski made his Major League debut at Citi Field on June 24 against the Los Angeles Dodgers, grounding out as a pinch hitter.