Former AC Milan manager Leonardo was named coach of city rival Inter Milan on Friday.
The European and Italian champion announced Leonardo's appointment on its website, a day after Rafa Benitez's contract was terminated by mutual agreement. Leonardo's contract starts Dec. 29 and runs until June 2012.
His first match in charge will come against second-place Napoli when Serie A resumes Jan. 6.
Benitez led Inter to the Club World Cup title last weekend, but the team is languishing in seventh place in Serie A, 13 points behind leader Milan. Benitez lasted only six months after taking over from Jose Mourinho, who left for Real Madrid following last season's historic treble.
Leonardo's only head coaching experience came last season when he led Milan, but the term ended abruptly when the 41-year-old Brazilian clashed with club owner and Italian Premier Silvio Berlusconi.
In its statement, Inter said it was "convinced that he'll be able to put his class, experience as a champion and mentality to the service of the club to get the results that Inter and its fans want."
Leonardo becomes the fifth coach to make the move from Milan to Inter, following Giuseppe Bigogno, Giovanni Trapattoni, Ilario Castagner and Alberto Zaccheroni.
He played for Milan for four years between 1997 and 2001 before returning to Brazil and working in a scouting role, in which he helped Milan secure the signings of Kaka and Alexandre Pato.
In 2008, he was appointed as Milan's technical director, then received his first coaching position in the wake of Carlo Ancelotti's departure to Chelsea.
After a difficult start last season, including a 4-0 rout by Inter, Leonardo began to build success with Milan by relying on an attack-oriented 4-2-1-3 formation that allowed players like Andrea Pirlo, Clarence Seedorf and Ronaldinho to line up together.
The attacking style reached its high point with a 3-2 win over Real Madrid at the Santiago Bernabeu stadium but the Rossoneri were eventually eliminated from Europe by Manchester United and Berlusconi grew increasingly agitated as he watched Inter storm to the Serie A, Italian Cup and Champions League titles - becoming the first Italian club to achieve the treble.
Now, Leonardo will be charged with restoring Inter to last season's form.
