After going undrafted in the MLB Draft, he signed with the Auckland Tuatara of the Australian Baseball League.
[1] On January 31, 2019, Marklund signed a minor league contract with the Kansas City Royals after he impressed them in a tryout.
[4] Marklund made his debut in the Royals organization with the Single–A Lexington Legends, compiling a 4–0 record and 0.46 ERA with 44 strikeouts and 6 saves across 39+1⁄3 innings pitched.
[5] Marklund did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.
[8] On April 27, 2023, Marklund signed with the Winnipeg Goldeyes of the American Association of Professional Baseball.