Houston Astros Mengden was drafted by the
Houston Astros in the fourth round, with the 106th overall selection, of the
2014 Major League Baseball draft. He made his professional debut with the rookie-level
Gulf Coast League Astros and was later promoted to the Low-A
Tri-City ValleyCats. In 2015, Mengden started the season with the Single-A
Quad Cities River Bandits and was promoted to the High-A
Lancaster JetHawks after recording a 1.16 ERA. In 10 games (8 starts) for Lancaster, he compiled a 2-1 record and 5.26 ERA with 48 strikeouts across innings pitched.
Oakland Athletics On July 23, 2015, the Astros traded Mengden and
Jacob Nottingham to the
Oakland Athletics in exchange for
Scott Kazmir. in 2016 In 2016, Mengden began the season with the
Double-A Midland RockHounds, but was promoted to the
Triple-A Nashville Sounds on May 1. With Nashville, he had a 3–1 record with a 1.39 ERA in seven starts. He won his first MLB game in the
Battle of the Bay against the
San Francisco Giants on June 27. Mengden would remain in the rotation for the remainder of the 2016 season, finishing with 14 starts for the A's. Mengden recorded 2 wins and 9 losses with 71 strikeouts in 72 innings. In 2017, Mengden spent the majority of the season in the minors, only making 7 starts for Oakland. In 2018, he was 7-6 with an ERA of 4.05 and 72 strikeouts in 22 games (17 starts). In 2019, Mengden did not replicate his success as he had done the previous season, going 5-2 with an ERA of 4.83 and 42 strikeouts in 13 games (9 starts). On October 9, Mengden elected free agency. Mengden was selected to the 40-man roster on June 13 after
Joel Payamps was placed on the
COVID-19 injured list. He cleared waivers and was sent outright to the Triple–A
Omaha Storm Chasers on July 2. On September 1, Mengden was selected back to the major league roster to make a spot start against the
Chicago White Sox. He went innings and allowed 3 runs on 5 hits with 2 strikeouts, taking the loss. Mengden was designated for assignment by the Royals the following day. He was again sent outright to Triple–A Omaha on September 4. He elected free agency on October 6. On March 29, 2023, Mengden re-signed with the Royals on a minor league deal. In 6 games (3 starts) for Omaha, Mengden struggled to a 7.36 ERA with 14 strikeouts across innings of work. He was released by the Royals organization on June 27.
Washington Nationals On July 2, 2023, Mengden signed a minor league contract with the
Washington Nationals organization. In 22 games for the Triple–A
Rochester Red Wings, he recorded a 7.20 ERA with 30 strikeouts across 35 innings of work. Mengden elected free agency following the season on November 6.
CTBC Brothers On January 17, 2024, Mengden signed with the
CTBC Brothers of the
Chinese Professional Baseball League. In 25 starts for the team, he compiled a 10–3 record and 2.86 ERA with 114 strikeouts across 154 innings pitched. With the Brothers, Mengden won the 2024
Taiwan Series. On January 23, 2025, Mengden re-signed with the Brothers. On March 5, Mengden was released by the Brothers due to failing an internal drug test.
Tecolotes de los Dos Laredos On March 11, 2025, Mengden signed with the
Tecolotes de los Dos Laredos of the
Mexican League. On June 26, Mengden signed a minor league contract with the
Arizona Diamondbacks; however, the transaction never materialized, and Mengden was reactivated by the team on July 5. In 17 starts he threw 90 innings going 8-5 with a 4.00 ERA with 67 strikeouts and also throwing a complete game shutout. ==Personal life==