The Nationals selected Parker's contract from Triple-A Rochester on Tuesday, Andrew Golden of The Washington Post reports.
Parker is now on the 40-man roster and protected from the Rule 5 Draft. The 24-year-old southpaw collected a 4.72 ERA and 150:61 K:BB over 124 innings between Double-A Harrisburg and Rochester in 2023. He'll likely return to Rochester to begin next season.