To acquire Pennington and infield prospect Yordy Cabrera, the D-backs sent outfielder Chris Young and $500,000 to the A's.
Arizona then sent Cabrera to the Marlins for Bell. The D-backs also received cash from the Marlins in the trade. The D-backs will pay $13 million of the $21 million that is still owed to Bell.
"We've addressed two needs today," D-backs executive vice president and general manager Kevin Towers said. "We knew we had an abundance of outfielders, and we wanted to add another strong arm in the pen, and we wanted to add some depth to the middle of the infield. We looked at the free agent market ... and what was available in trade, we felt Cliff was one of the better options we had."
Bell reunites with Kevin Towers, who acquired Bell in December 2006 when Towers was the GM of the Padres. Bell had his best years with the Padres, saving 42, 47 and 43 games from 2009-11.
The 35-year-old righty parlayed that success into a three-year, $27 million free-agent deal with the Marlins this past offseason.
Bell struggled from the outset in Miami, lost his closer's job and ultimately finished the season with a 5.09 ERA and 19 saves in 73 appearances. He also had a public falling out with Miami manager Ozzie Guillen in September.
"In my mind, as well as I know him since the velocity is still good and he's still got the good rotation on the breaking ball, I think changing scenery and getting back into hopefully a comfortable environment for him, I think he'll be strong," Towers said of Bell. "I don't think there's a lot you have to do in the way of tweaking where he's at. I think it's just really getting back to where he was before, challenging hitters and throwing to contact and going right after them."
While he was asked to close in his last few years in San Diego and at the beginning of last season in Miami, Bell will most likely pitch in the seventh inning for the D-backs, with David Hernandez the primary eighth inning guy and J.J. Putz remaining as closer.
Towers said he told Bell that Putz would remain the closer, and that Bell said he was just looking forward to the new opportunity. Bell was used as a setup man early in his career in San Diego for closer Trevor Hoffman.
Bell's contract calls for salaries of $9 million in 2013 and '14, and his $9 million option for '15 becomes guaranteed if he finishes 55 games in '14 or combines to finish 100 games between '13-14.
Pennington, 28, helps the D-backs improve their depth at shortstop with the departure of Stephen Drew, who was dealt to the A's in August and is now a free agent.
Pennington, who hit .215 in 462 plate appearances last year, is a good defender and joins Willie Bloomquist and John McDonald at the position.
Shortstop was the D-backs' primary area of need this offseason, as the club did not feel it could rely on Bloomquist and McDonald to handle the load. Pennington, who is eligible for salary arbitration for the first time this year, gives the D-backs a chance to bring Double-A shortstop Chris Owings along at a slower pace.
"Playing against those guys this year, obviously a team that I thought was really talented and thought had a lot of potential and to be able to join that team now and go forward, I'm really excited about the chance to win some ballgames and get back to the postseason and play some fun games," Pennington said.
While he crossed off a couple of things on his to-do list with the moves, Towers still would like to add a late-inning left-hander to the bullpen. In addition, he will look to see if there is an upgrade over Chris Johnson available at third base, and whether or not there's a veteran who can be added to the starting rotation.
With Justin Upton, Jason Kubel, Gerardo Parra and Adam Eaton in the outfield, not to mention rookie A.J. Pollock, it seems the D-backs could still make another move with an outfielder, but Towers didn't make it seem imminent.
"As of now more than likely, yes," Towers said when asked if it was possible he wouldn't deal another outfielder. "We feel pretty good where we're at right now. I can't anticipate what's going to happen in the next couple of months, as we go to the GM Meetings and the Winter Meetings and people approach you about trades. I think I always have to keep my ears open and listen to what people have to say."