The 41-year-old, who was appointed in January on a contract running until June 2032, departs less than four months into the role.
While the club had no immediate plans to assess his position, a sharp downturn in performances forced an early decision.
Calum McFarlane has been placed in temporary charge until the end of the season, when the club is expected to explore long-term options and appoint a fifth permanent manager under the BlueCo ownership.
McFarlane previously stepped in after Enzo Maresca left on New Year’s Day and managed a 1-1 draw against Manchester City at the Etihad.
In an official statement, the club said the decision was difficult but necessary, citing performances and results that have fallen short of expectations at a crucial stage of the season.
A 1-0 loss to Brighton & Hove Albion on Tuesday marked a fifth consecutive league defeat without scoring — a streak not seen since 1912. Rosenior openly criticised himself and his squad after the match, while club executives spent the following day weighing their options.
Their focus now shifts to securing victory in Sunday’s FA Cup semi-final against Leeds United and pushing for qualification to next season’s UEFA Champions League.
Despite winning his first four Premier League matches in charge, a 2-2 draw with Leeds on February 10 triggered a slump that yielded just one win and five points from nine games. That dip has seen Chelsea fall to seventh in the table, seven points adrift of the top five and only three points above Fulham FC in 12th.
Rosenior’s tenure also included an 8-2 aggregate defeat to Paris Saint-Germain in the Champions League round of 16, as well as two losses to Arsenal FC in the Carabao Cup semi-finals.
Chelsea’s route to the FA Cup semi-finals has come without beating a Premier League side. After facing Leeds, they return to league action against Nottingham Forest on May 4, before concluding their season against Liverpool FC, Tottenham Hotspur, and Sunderland AFC