The deal comes two years after the Dolphins acquired Marshall from Denver for a pair of second-round picks.
In his two seasons in Miami, Marshall reached 80 catches and 1,000 yards and he was named the Pro Bowl MVP in February after setting a game record with four touchdown catches.
But Marshall also was very expensive, having signed a four-year extension with the Dolphins after the trade from Denver.
Trading Marshall frees up cap space for the Dolphins and will allow them to make some moves they otherwise might have had a problem making.
On the flip side, the trade leaves the Dolphins without a true No. 1 receiver, so unless they're able to land Vincent Jackson or Reggie Wayne in free agency, that might jump to the top of the list of priorities come draft day.