Hasenhuttl leaves the Saint Mary's Stadium with Southampton in the relegation zone after just three wins in their 14 games played.
Sunday's 4-1 loss at home to Newcastle United proved to be Hasenhuttl's final game in charge of the Saints.
The 55-year-old Austrian was first handed the Saints job in December 2018, taking over from Mark Hughes.
A statement from the club read: " Southampton Football Club can confirm it has parted company with Men’s First Team Manager Ralph Hasenhüttl. First Team Assistant Coach Richard Kitzbichler has also today left the club.
"Hasenhüttl, who was appointed in December 2018, departs having made a significant contribution to the club, overseeing some memorable results and also playing a key role in the development of our club infrastructure, identity and playing squad.
"However, we now believe it is an appropriate time to make a change. Everyone involved with the club would like to express their sincere thanks to Ralph for all of his efforts, as well as the unwavering commitment he has shown throughout his time as manager.
"First Team Lead Coach Rubén Sellés will take charge of the side on an interim basis for our game on Wednesday night. The club will be announcing a permanent replacement in due course."
Hasenhuttl is the Premier League's fifth managerial casualty this season after Scott Parker, Thomas Tuchel, Bruno Lage and Steven Gerrard.
