A 15-year veteran, Polanco spent the past three seasons with the Phillies.
Since trading Yunel Escobar during the Winter Meetings for prospect Derek Dietrich, the Marlins have been aggressively seeking a third baseman with a track record.
The Marlins have liked Polanco for a while. The question was his health.
In 2012, Polanco was bothered by back injuries, and he appeared in 90 games, batting .257 with two home runs and 19 RBIs.
Lower back problems also plagued him in 2011, a season during which he also dealt with a sports hernia injury.
When healthy, Polanco has been highly productive.
He's a proven winner, being part of five postseason teams. While with the Tigers in 2006, he was named the American League Championship Series MVP.
But avoiding the disabled list has been an issue.
Since playing in 153 games for the Tigers in 2009, Polanco has played in 132 games in 2010, 122 in '11 and 90 a year ago.
Polanco is the second member of the 2012 Phillies to sign with Miami as a free agent. Previously, the Marlins signed left fielder Juan Pierre.
After trading Escobar, the Marlins made it clear they were reinvesting his projected $5 million back into the payroll.
The remainder of the $5 million may be spent to address other areas of the ballclub, like a relief pitcher.
Before locking up Polanco, the Marlins also considered signing Miguel Tejada, the 38-year-old former All-Star and American League MVP.
Tejada last played in the big leagues in 2011.
The Marlins recently scouted Tejada, who is playing winter ball for Aguilas Cibaenas in the Dominican Republic.
Tejada spent 15 years in the big leagues, breaking in with the A's in 1997 while also playing for the Orioles, Astros, Padres and Giants. It's unclear if the Marlins would consider offering Tejada a Minor League contract with an invitation to Spring Training.
At the Winter Meetings, the Marlins made offers to several free agents, including Jeff Keppinger and Mark Reynolds. But both signed elsewhere.
Signing Polanco allows the Marlins to use Greg Dobbs in the role he is best suited -- a left-handed bat off the bench.
Dobbs was a possible choice to see regular action at third base if a more established veteran wasn't added.
When Spring Training gets under way, the Marlins will also have several internal candidates who will see action at third base -- Kevin Kouzmanoff, Zack Cox and possibly Chris Coghlan.