The Marlins tweeted a picture of Jeter sitting behind a desk shortly after his group closed on its purchase of the team on Tuesday.
Jeter also penned a brief letter that was posted on The Players' Tribune, a site he founded.
"Our ownership group is focused on building a team that this community can be proud of," the former New York Yankees shortstop wrote. "We believe in Miami, we believe in this organization and, with your help, we believe we will turn it around."
Jeter also recalled a recruiting trip he made to the University of Miami as a teenager from Kalamazoo, Mich.
"I was only 17 and Miami was the farthest I'd ever been from home," Jeter said. "It wasn't just that hearing Spanish was new to me. Everything about Miami was different and exciting. I don't really recall exactly what I did or where I went that weekend. It was a blur.
"But to this day I still remember how it felt. The music, the weather, the diversity -- I remember how alive Miami was.
"One thing really jumped out at me. It was the way people talked about Miami -- with such a sense of pride. Everyone I met seemed to go out of their way to tell me why their city was so special."
Major League Baseball announced Wednesday its owners unanimously approved the sale of the Marlins to the group led by venture capitalist Bruce Sherman and Jeter, who will be the CEO.
Sherman and Jeter officially take over upon the close of the $1.2 billion deal. The price tag is the second-highest in a history for an MLB team, behind only the Los Angeles Dodgers' $2 billion sale in 2012.
Jeffrey Loria purchased the team for $158.5 million in February 2002, and a year later, the then-Florida Marlins won their second World Series. The Marlins haven't been back in the playoffs since, and they haven't finished above .500 since 2009.
The Marlins had a team-record $115 million payroll on Opening Day this year.