Plachta played for Schwenningen and Mannheim as a junior and made his debut in Germany's second division for Heilbronn during the 2008–09 season. The following season, he logged first minutes in Germany's top-flight
Deutsche Eishockey Liga (DEL) with
Adler Mannheim. After six seasons in the DEL, including winning the title with Mannheim in 2015, and having secured a role in the
German national team, Plachta was signed to a one-year entry-level contract with the
Arizona Coyotes of the
National Hockey League (NHL) on 28 May 2015. In his debut North American season in
2015–16, Plachta was assigned to Arizona's AHL affiliate, the
Springfield Falcons. In 46 games with the Falcons, Plachta compiled two goals and 7 points before the Coyotes traded him on trade deadline day along with a conditional 7th-round draft pick in
2017 to the
Pittsburgh Penguins in exchange for
Sergei Plotnikov on 29 February 2016. Plachta played a total of 30 contests for Pittsburgh's AHL affiliate
Wilkes-Barre Scranton Penguins during the season. Having not been allowed to play in the NHL during the season, and with Pittsburgh opting not to extend a qualifying offer, Plachta returned to Germany, returning to Adler Mannheim on 30 June 2016 with the signing of a four-year deal. ==International play==