Moniak attended La Costa Canyon High School in Carlsbad, California, and played center field for the baseball team.

He hit .270/.304/.383 with 28 doubles (second in the Florida State League), five home runs, 55 RBI, six stolen bases, and seven sacrifice flies (tied for 5th) in 433 at bats in 114 games.

[23] That night, he made his MLB debut against the New York Mets as a ninth-inning pinch runner for Alec Bohm, at Citizens Bank Park.

[24] On September 18, 2020, Moniak roped a line drive into right field, a single, for his first big league hit, in the second game of a doubleheader against the Toronto Blue Jays.

[25] On April 21, 2021, Moniak hit his first major league home run in the 2nd inning against Anthony DeSclafani of the San Francisco Giants.

However, Moniak suffered a right hand fracture in the final exhibition game against the Tampa Bay Rays on a Ryan Yarbrough hit-by-pitch.

On August 6, during a game against the Seattle Mariners, Moniak injured his left middle finger while attempting to bunt.

[32] He was recalled from Salt Lake on May 12, 2023, hitting .280 with fourteen home runs and forty-five RBIs in eighty-five games.