Chelsea appoint Rosenior as new boss
The 41-year-old said earlier Tuesday during a farewell press conference at Ligue 1 club Strasbourg that he had "verbally agreed" on the move to Stamford Bridge.
The move was rubber-stamped shortly afterwards.
"I am extremely humbled and honoured to be appointed head coach of Chelsea Football Club," Rosenior said in a statement on Chelsea's website.
"This is a club with a unique spirit and a proud history of winning trophies.
"My job is to protect that identity and create a team that reflects these values in every game we play as we continue winning trophies."
Rosenior has just three years' experience as a manager and has never coached in the Premier League.
He had been widely touted as the frontrunner to succeed Maresca since the Italian was sacked on Thursday.
Strasbourg and Chelsea are owned by the same consortium, BlueCo.
The former Hull City manager will become Chelsea's fourth permanent boss since BlueCo took control of the Londoners in 2022.
Rosenior said he had wanted to announce the news himself in Strasbourg because of his deep feelings for the club.
"Everything is agreed and it will probably go through in the next few hours," he told reporters.
"I'm here because I care about this club and I felt it was right to answer your questions physically here today before I move on."
Rosenior, whose father Leroy was also a player and then a manager, has never faced the kind of media glare that will await him in west London.
"I'm so excited about the future. I cannot lie. My whole life I've worked to be a coach," he said.
"To be presented with this opportunity to manage a world-class football club is something I've always dreamed of.
"With that is a mixed emotion of sadness of what I'm leaving behind."
Rosenior played in the Premier League and Championship. His clubs included Fulham, Reading and Hull City.
He worked as a coach at Derby under Phillip Cocu and Wayne Rooney.
He briefly replaced Rooney on an interim basis in 2022 and later that year took over as manager of Hull in the Championship, England's second flight.
He was sacked after 18 months and in July 2024 was appointed by Strasbourg, who he guided to seventh place in Ligue 1 last season.
Maresca won the UEFA Conference League and Club World Cup during his first season at Stamford Bridge.
But tensions emerged in recent weeks and his reign came to an abrupt end on New Year's Day.
Under-21s coach Calum McFarlane took charge of Chelsea for Sunday's 1-1 draw at Manchester City.
They travel to London rivals Fulham on Wednesday.