Pettini takes Leicestershire white-ball captaincy
Pettini, 32, joined Leicestershire from Essex after the 2015 season. In 2008, Pettini, who was the youngest captain on the county circuit when he replaced Ronnie Irani, led Essex to the Friends Provident Trophy which remains the clubs most recent silverware.
Pettini's vice-captain in the Royal London Cup and the NatWest T20 Blast will be Australian pace bowler Clint McKay while another of Leicestershire's winter signings, Paul Horton who arrived from Lancashire, will be vice-captain to Cosgrove in four-day cricket.
Andrew McDonald, the performance director, said: "We have completed our player recruitment for the 2016 season and have now put our leadership group in place for the 2016 season.
"Mark Cosgrove will continue to lead us in four-day cricket and Mark Pettini will take the reins in one-day cricket. Paul Horton and Clint McKay will support them in their respective roles of vice-captain but I am looking for leadership throughout the playing group.
"We had some fantastic candidates in the ranks and the most important thing we are stressing is that you don't need a title after your name to be a leader. We can only name one captain and vice-captain in each format but we have lots of experienced players in the ranks and I expect leadership contributions to come from a variety of sources."