Rosenior lasted less than four months in the role after his January appointment following Enzo Maresca's departure, becoming the latest casualty of Chelsea's turbulent season after seven defeats in their last eight matches across all competitions.
Rosenior's dismissal on Wednesday came a day after a humiliating 3-0 loss at Brighton & Hove Albion took their losing streak to five matches and ensured the south-coast club leapfrogged Chelsea into sixth place in the table.
Chelsea are now seven points behind fifth-placed Liverpool, who have a game in hand.
The five-game losing streak is Chelsea's worst since 1912 — the same year, Blues' fans have noted gloomily, that the Titanic sank.
"Chelsea Football Club has today parted company with Head Coach Liam Rosenior," the club said in a statement.
"On behalf of everyone at Chelsea FC, we would like to place on record our gratitude to Liam and his staff for all their efforts during their time with the Club.
"This has not been a decision the Club has taken lightly, however recent results and performances have fallen below the necessary standards with still so much more to play for this season."
The club said Calum McFarlane would take charge of the team as interim head coach until the end of the season, including their FA Cup semi-final at the weekend against Leeds.
Rosenior started impressively with a run of six wins in seven games, but things unravelled quickly in recent weeks, including elimination from the Champions League at the hands of Paris Saint-Germain.
Rosenior becomes the fifth permanent manager to lose his job since US owners Clearlake and Todd Boehly bought Chelsea in 2022.
"As the club works to bring stability to the head coach position, we will undertake a process of self-reflection to make the right long-term appointment," Chelsea said.
While there have been trophies -- the Club World Cup and Europa Conference League were collected last season -- this could be the third campaign out of four in which Chelsea have failed to qualify for the Champions League.
Under former Russian owner Roman Abramovich, Chelsea were one of the most dominant teams in Europe, winning a full set of trophies, including two Champions Leagues and five Premier League titles.
They last won the Champions League in 2021, the year before Abramovich was forced to sell the club after being sanctioned by the British government in the wake of Russia's war with Ukraine.
