According to multiple reports and sources, Bell agreed Thursday night to a three-year, $27 million deal with a vesting option for a fourth season.
The deal is pending the 34-year-old closer completing his physical.
Marlins executives will be arriving at the Winter Meetings in Dallas on Monday afternoon.
Bell has recorded 132 of his 134 career saves with the Padres over the last three seasons, and he fills the team's need at closer.
Per team policy, the Marlins don't talk about specific signings until everything is completed.
Barring anything unforeseen, an announcement on Bell should be in the next few days.
Along with adding a closer, the Marlins also are heavily pursuing other free agents, like Mets free-agent shortstop Jose Reyes and Rangers lefty C.J. Wilson.
White Sox lefty Mark Buehrle is on the Marlins' wish list, although there is plenty of competition for his services. It's also believed Buehrle is seeking a no-trade clause, which is something Miami doesn't normally do. For instance, when Carlos Delgado signed a four-year, $52 million contract in 2005, he didn't have a no-trade provision.
Speaking generally about free agents and trade possibilities, Beinfest said the Winter Meetings are usually when deals get done.
"We're having conversations with free agents," Beinfest said. "We're having conversations with teams. We've looked at everything. It's very fair to say that right up to now, and through the weekend and into Dallas, we'll continue on that path.
"There has been chatter on both fronts. It's normal this time of year, you better be on the phone. You better be working, because this is the time you hopefully can achieve your offseason goals. It's the heart of the offseason in a lot of ways for most teams."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro. This story was not subject to the approval of Major League Baseball or its clubs.