“I’m here because I care about this club [Strasbourg] and I felt it was right to answer your questions physically here today before I move on.”
Rosenior said Strasbourg first-team coach Kalifa Cisse, assistant head coach Justin Walker and head of analysis Ben Warner will join him at Chelsea.
Ronseior joined Strasbourg in July 2024 and guided the French club to seventh in Ligue 1 last season, securing European football for the first time in eight years.
His final match was a 1-1 draw at Nice on Saturday, their fifth league game without a win.
They are seventh in Ligue 1 and top of the Conference League.
“The last 18 months have been a joy and the best of my professional career,” Ronseior said.
“I will love this club for the rest of my life but I cannot turn down Chelsea.”
The former Fulham and Hull full-back has never managed in the Premier League but previously coached in the Championship with Derby County and the Tigers.
“I would not have accepted the Chelsea job if I was not ready,” Rosenior said.
“There are clubs you just cannot turn down. I hope the Strasbourg fans can see that and be proud of that.”
He added: “I have had interest from many clubs, including Champions League clubs, which I have always been open with to [our president] Marc [Keller] and our ownership.”
Chelsea sit fifth in the Premier League before their game against Fulham at Craven Cottage on Wednesday (19:30 GMT).
Caretaker manager Calum McFarlane was in place for Chelsea’s 1-1 draw at Manchester City.
