Thomas Diethart (born 25 February 1992) is an Austrian former ski jumper who won the 2014 Four Hills Tournament.

Diethart's debut in the FIS Ski Jumping World Cup took place in January 2011 in Innsbruck.

His first world cup win took place just a few days later in Garmisch-Partenkirchen, when he won against his teammate Thomas Morgenstern and the Swiss Simon Ammann.

After a 5th place in Innsbruck, he proceeded to win his second world cup jump in Bischofshofen, which also meant the triumph of the well-respected Four Hills Tournament.

Diethart competed for Austria at the 2014 Winter Olympics in Sochi, Russia in men's ski jumping in both the individual normal hill and large hill events.