Italian FA commissioner Roberto Fabbricini said Mancini had proved his "great desire" to become the new Italy coach. Gli Azzurri sacked Ventura after failing to qualify for this summer's World Cup.
"I want to be a good coach and take Italy back to the top of the world and of Europe", Mancini said at his presentation at the Italian Soccer Federation's Coverciano centre near Florence. The former Zenit boss, who has agreed to a contract of 2 years has the responsibility to rebuild the national side and to qualify for the 2020 European championship.
It will be a first role in worldwide management for Mancini, who has left Russian club Zenit St Petersburg to take up the post.
He signed his new deal later in the day.
His first matches in charge will come against Saudi Arabia on May 28, France on June 1 and the Netherlands on June 4.
He will also prepare Italy for a friendly against France on June 1 in Turin which could be the final worldwide game for goalkeeping legend Gianluigi Buffon.
He led Manchester City to their first English league title in 44 years in 2012, and won 3 Serie A titles with Inter Milan.
Since then Mancini has guided Galatasary to Turkish Cup glory before steadying the ship in his second stint at Inter Milan.
Mancini, a gifted forward in his playing days, won a surprisingly modest 36 caps for Italy and never played at a World Cup, although he was an unused member of the 1990 squad.
His Zenit team finished the Russian Premier League in fifth after beating relegated SKA Khabarovsk 6-0 on Sunday.
He never became a regular with Italy having a love-hate relationship with the national side during his 10-year global playing career, during which he won 36 caps and scored 4 goals.