In 2017, Fermín played in 47 games for the rookie-level Idaho Falls Chukars, slashing .282/.403/.356 with one home run and 39 RBI.

He split the 2018 season between Idaho Falls and the rookie-level Burlington Royals, posting a cumulative .249/.346/.350 slash line with 2 home runs and 19 RBI.

In 2019, Fermín split the season between the Single-A Lexington Legends and the Double-A Northwest Arkansas Naturals, hitting .260/.298/.418 with career-highs in home runs (12) and RBI (41) in 86 games between the two affiliates.

[2] In 2021 he spent time with Northwest Arkansas and the Triple-A Omaha Storm Chasers, batting .277/.355/.440 with 10 home runs and 47 RBI in 77 contests.

On July 14, 2022, Fermín was selected to the 40-man roster and called up to the majors for the first time after multiple players were placed on the restricted list prior to a series in Canada against the Toronto Blue Jays.