[2][3][4] He made his professional debut with the Gulf Coast Astros and was later promoted to the Tri-City ValleyCats.

In 2015, he started the season with the Quad Cities River Bandits and was promoted to the Lancaster JetHawks after recording a 1.16 ERA.

[5][6] On July 23, 2015, the Astros traded Mengden and Jacob Nottingham to the Oakland Athletics in exchange for Scott Kazmir.

[7] In 2016, he began the season with the Double-A Midland RockHounds, but was promoted to the Triple-A Nashville Sounds on May 1.

On December 25, 2020, Mengden signed a one-year, $725,000 guaranteed contract plus $275,000 possible performance incentives with the Kia Tigers of the KBO League.

[14] Mengden was selected to the 40-man roster on June 13 after Joel Payamps was placed on the COVID-19 injured list.

On September 1, Mengden was selected back to the major league roster to make a spot start against the Chicago White Sox.

[20] On July 2, 2023, Mengden signed a minor league contract with the Washington Nationals organization.

[22] On January 17, 2024, Mengden signed with the CTBC Brothers of the Chinese Professional Baseball League.