Fermín spent the 2018 season with the Low–A Mahoning Valley Scrappers, playing in 71 games and hitting .279/.391/.383 with two home runs, 26 RBI, and 17 stolen bases.[2] He played the 2019 season for the Single–A Lake County Captains, slashing .293/.374/.379 with six home runs, 41 RBI, and 28 stolen bases across 105 contests. Fermín did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[3]
Fermín returned to action in 2021, spending the year with the Double–A Akron RubberDucks as well as making four appearances for the Triple–A Columbus Clippers at the end of the year. In 84 games for Akron, he logged a .258/.329/.383 batting line with six home runs and 39 RBI.[4] Fermín spent the entirety of the 2022 season with Columbus, appearing in 90 games and hitting .215/.336/.322 with six home runs, 31 RBI, and nine stolen bases.[5]
St. Louis Cardinals
On November 9, 2022, the St. Louis Cardinals acquired Fermín from the Guardians and he was added to their 40-man roster.[6] Fermín suffered a quadriceps strain in spring training and was optioned to the Triple-A Memphis Redbirds to begin the 2023 season.[7]
On July 7, 2023, Fermín was promoted to the major leagues for the first time.[8] In 21 games for St. Louis, he batted .235/.339/.255 with no home runs and four RBI.
Fermín was optioned to Triple–A Memphis to begin the 2024 season.[9]