The firing of Jennings was announced just hours after Mattingly was hired, this after the team said he would retain his old front-office job. The old GM was under contract through 2018, was owed $4.5 million and managed the team after Mike Redmond was fired following a 16-22 start.
Many believe Jennings moving to the dugout is what ruined his relationship with team owner Jeffrey Loria, leading to him being relieved of his duties. President Michael Hill will assume the GM position.
Mattingly's deal is worth four years, but the official announcement of the move will not be made until after the World Series.
The former New York Yankee stepped down as manager of the Los Angeles Dodgers on October 22nd with one year left on his deal, this after his team was eliminated by the New York Mets.
Mattingly went 446-363 in five seasons with the Dodgers, including three straight National League West division titles, but struggled with an 8-11 postseason record.
He will be the eighth Marlins' manager since 2010, and 15th manager since the franchise's inception in 1993. Just five of those managers have managed at least 100 games with Miami, and Mattingly expects to be the sixth. Of those five, only Jack McKeon had a winning record of 281-257 in four seasons.
The Marlins have been in a tailspin since falling in the 2003 World Series, and they have great hope that they have found the man to turn things around starting in 2016. Mattingly, along with young stars Jose Fernandez and Giancarlo Stanton, look to help the franchise regroup 71-91 record in 2015, their sixth consecutive losing season.