Marshall will fly to Miami later Wednesday for a physical, after which he is expected to sign a long-term contract that he's been seeking for over a year.
Marshall has long wanted out of Denver, and got his wish when the Broncos pulled off their second blockbuster deal in as many seasons under coach Josh McDaniels. Denver sent quarterback Jay Cutler to Chicago last April for Kyle Orton and draft picks.
Marshall's four-year stint in Denver was filled with fantastic plays but also plenty of frustration.
He posted his third consecutive 100-catch season last year and made his second straight trip to the Pro Bowl despite several run-ins with McDaniels both on and off the field. He was suspended for insubordination in training camp and again for the season finale after he was tardy for treatment on a hamstring injury the team felt he was exaggerating.
Still, Marshall caught 101 passes last season, including an NFL-record 21 in a loss at Indianapolis, for 1,120 yards. His 10 touchdowns were a career best.
Miami is a surprise destination for Marshall because Dolphins coach Tony Sparano hadn't shown much interest in acquiring him. But football czar Bill Parcells, who has final say on personnel matters in Miami, has never shied away from talented-but-troubled wide receivers, working with Terry Glenn in New England, Keyshawn Johnson in New York and Terrell Owens in Dallas.
Marshall, who has 327 career catches for 4,019 yards and 25 touchdowns in four seasons, represents the biggest trade acquisition by the Dolphins since running back Ricky Williams went to Miami in 2002 for four draft picks, including two first-rounders.
The trade also shakes things up in the AFC East, where the New York Jets acquired another talented but troubled wide receiver in Santonio Holmes from the Pittsburgh Steelers on Sunday in exchange for a fifth-round pick in this year's draft.
The Dolphins have been desperate for a deep threat at receiver to loosen up defenses for their potentially potent ground game and young, strong-armed quarterback Chad Henne.
Speedy Ted Ginn Jr. has been a disappointment since Miami took him with the ninth overall draft pick in 2007. Ginn and the other wideouts Brian Hartline, Davone Bess and Greg Camarillo combined for only six touchdown catches last season.
The acquisition of a top-line receiver frees up the Dolphins to use the No. 12 pick in the draft next week on the defensive front seven, where help is also needed.
The Broncos, who own the 11th pick in the first round, have many needs, especially at linebacker, but now will likely address wide receiver in the draft, as well.
Marshall's departure removes Orton's primary target and leaves the Broncos with Jabar Gaffney, who had 54 catches for 732 yards and two TDs last season, as their top receiver. Eddie Royal caught 37 passes with no TDs and Brandon Stokley had 19 catches, four for TDs.
In March, the Broncos slapped a first-round tender on Marshall, but teams were unwilling to part with a first-round draft pick as compensation to lure the restricted free agent out of Denver.
The Seattle Seahawks were the only team that had Marshall in for a visit during free agency, flying him in on a seaplane. The Seahawks, however, were unwilling to part with the sixth pick in the upcoming draft to sign him.
Marshall signed his $2.521 million tender on Tuesday to help facilitate a trade.
For all his talents on the field, Marshall has had several run-ins with police and visits to commissioner Roger Goodell's office to discuss his off-the-field behavior. He was suspended for the 2008 opener following a series of domestic disputes involving a former girlfriend.
In February, an emotional Marshall was a witness in the murder trial of Willie Clark, who was convicted in the 2007 drive-by slaying of Broncos cornerback Darrent Williams.
Last summer, Marshall was suspended by the team for throwing a tantrum at practice during training camp. The source of his frustration was twofold: he was upset with the team's medical staff for misdiagnosing a hip injury that required offseason surgery and he was displeased with his contract.
Marshall earned $2.2 million last season in the final year of the rookie deal he signed in 2006 as a fourth-round draft pick out of Central Florida.