The deal is very good from an economics standpoint. McNown will count only $389,000 against the Dolphins salary cap for each of the next three seasons.
"We're getting a first-round quarterback for pretty much the minimum," said Dolphins vice president of player personnel Rick Spielman, who was in Chicago when the Bears made McNown the 12th overall pick in the 1999 draft.
Spielman said the deal was consummated after both sides found a way to reduce their risks.
The McNown discussions began on the first weekend of the preseason when Spielman flew out to watch Chicago play Cincinnati and told new Bears GM Jerry Angelo to give him a call if McNown ever became available.
McNown was told of the trade during a team meeting with the Bears and immediately left. He was scheduled to fly to Miami Wednesday and will take a physical on Thursday.
McNown was not available for comment Wednesday, but figures to talk to the media on Thursday.
Spielman and Coach Dave Wannstedt both talked to McNown on Wednesday.
"He's just relieved he's going to get a fresh start somewhere," Spielman said. "The kid is very excited about coming down here and working with Chan Gailey and Mike Shula, who are both very good at developing quarterbacks.
"It's an ideal situation if he takes advantage of the opportunity. If not, we'll go from there."