He has previously played in Major League Baseball (MLB) for the Baltimore Orioles, Miami Marlins, and Tampa Bay Rays.

[2] He made his professional debut with the Aberdeen IronBirds and also spent time with the Delmarva Shorebirds; in ten total games between the two teams, he pitched to a 2–1 record and 3.24 ERA.

[8] Hess made his major league debut on May 12, 2018[9] against the Tampa Bay Rays at Oriole Park at Camden Yards.

In his first start of the 2019 season in a 6–5 win over the Toronto Blue Jays at Rogers Centre on April 1, Hess had a no-hit bid through 6 1/3 innings before being removed by manager Brandon Hyde in favor of Pedro Araújo.

[10] With his record at 1–10 by the end of the campaign, he and Gabriel Ynoa became the first pair of teammates with double-digit losses and no more than one win since Jack Nabors and Tom Sheehan of the 1916 Philadelphia Athletics.

[18] On August 19, 2021, Hess signed a minor league deal to return to the Tampa Bay Rays and was assigned to Triple-A Durham.

On October 14, Hess elected free agency,[24] before re-signing with the Rays on a minor league deal on November 11.

[27] On October 13, 2021, Hess announced via Twitter that he will undergo chemotherapy after doctors discovered a cancerous germ cell tumor in his chest.