The former Italy midfielder had signed a two-year contract with the Londoners, the European champions said on their website.
Di Matteo, 42, is the eighth manager to have worked under Roman Abramovich since the Russian billionaire bought the Premier League club in 2003, following Claudio Ranieri, Jose Mourinho, Avram Grant, Luiz Felipe Scolari, Guus Hiddink, Carlo Ancelotti and Andre Villas-Boas.
"Roberto's quality was clear for all to see when he galvanised the squad last season and helped the club make history, and the owner and board are very pleased he will be continuing his good work," Chelsea's chief executive Ron Gourlay said on the website.
"We all believed he was a young coach with much to offer when we first asked him to take charge of team affairs in March and the manner in which he worked with us, the players and all the staff, and the success that followed, made him the clear choice when it came to selecting the person to take us forward in the seasons to come."
In March, Di Matteo was promoted from assistant coach to interim manager with the team in turmoil following the sacking of Portuguese Villas-Boas.
REMARKABLE TURNAROUND
The former Chelsea player sparked a remarkable turnaround in the club's fortunes in the final two months of the campaign.
Unifying a dressing room of players who appeared to have lost their way under Villas-Boas, Di Matteo guided the team to an against-the-odds triumph over favourites Barcelona in the semi-finals of the Champions League.
Then, on May 19, Chelsea lifted the European Cup for the first time after beating Bayern Munich in a penalty shootout in the final at the German club's Allianz Arena.
Two weeks earlier Di Matteo's side had beaten Liverpool 2-1 in the FA Cup final at Wembley.
"I'm obviously delighted to have been appointed as manager and first-team coach. We all achieved incredible success last season that made history for this great club," Di Matteo said.
"Our aim is to continue building on that and I'm already planning and looking forward to the squad's return for pre-season."
The Italian won the FA Cup as a player with Chelsea in 1997 and 2000, scoring in both finals against Middlesbrough and Aston Villa respectively.
Di Matteo, a great favourite of the fans, was also on target in the 1998 League Cup final win over Middlesbrough.
He suffered a triple leg fracture in a UEFA Cup tie in September 2000 and, after 18 months of battling against the injury, was forced to retire as a player at the age of 31.
