The Russian handed the former Liverpool boss a contract until the end of the season, having seemingly been unable to woo Pep Guardiola, the man said to be his number one target.
Announcing that Benitez was an "interim" rather than permanent appointment, Chelsea said in a statement: "Chelsea Football Club can confirm Rafael Benitez has been appointed interim first-team manager until the end of the season."
The statement continued: "The owner and the board believe that, in Benitez, we have a manager with significant experience at the highest level of football, who can come in and immediately help deliver our objectives.
"The 52-year-old Spaniard is due to meet the players at the training ground in Cobham tomorrow. The two-time UEFA Manager of the Year comes with outstanding pedigree.
"He began his managerial career in his homeland, most notably at Valencia where he built a reputation as one of Europe's top coaches by winning the Spanish League twice and the UEFA Cup. He then spent six years at Liverpool and led them to their fifth European Cup and an FA Cup."