McCarthy said the team will switch from a 4-3 defense, which utilizes four down linemen and three linebackers, to Capers' specialty, the 3-4 defense, which uses three linemen and four linebackers.
A news conference with Capers was scheduled for Tuesday morning.
McCarthy said one of the reasons he wants to change the Packers' defensive scheme is the challenges the offensive-minded coach had in trying to game-plan against it.
"From an offensive standpoint, it creates targeting problems," McCarthy said Monday, announcing Capers' hiring after the two reached an agreement in principle Sunday night. "That doesn't mean we won't line up in a four-man front [sometimes]. We'll move in and out of both four-man and three-man fronts.
"But it's an excellent run defense [and it] creates pass rush on the quarterback. From an offensive standpoint ... it really cuts the menu of the offense probably in half of what you would normally do [against] a four-man front."
Capers spent the past year as a special assistant and secondary coach of the New England Patriots. He is still owed $2.6 million by the Dolphins for the 2009 season; he was hired by Miami in 2006 and was defensive coordinator in 2007.
While the Packers are getting an undisclosed discounted salary for this year, a source said the team will pay Capers in excess of $2 million for 2010.
The 58-year-old Capers, the former Carolina Panthers and Houston Texans head coach replaces Bob Sanders, whom McCarthy fired Jan. 5, along with most of the defensive position coaches.
Capers interviewed with McCarthy on Friday and Saturday, after McCarthy had interviewed ex-49ers coach Mike Nolan, longtime NFL defensive coordinator Gregg Williams and former New Orleans Saints coach and St. Louis Rams interim coach Jim Haslett.
Giants coach Tom Coughlin targeted Capers as a replacement for Steve Spagnuolo, who was hired Saturday as head coach of the St. Louis Rams. However, while Giants ownership hesitated on the ultimate salary bid for a new defensive coordinator, Capers decided he did not want to wait and accepted the Packers' offer, sources said.
The Giants are now expected to promote a defensive assistant from within their own staff, but might consider outside candidates.
Capers had worked with Coughlin in Jacksonville in 1999 and 2000. He runs a hybrid 3-4 defensive scheme but primarily played a 4-3 under Coughlin with the Jaguars.
McCarthy said one of his top priorities was hiring someone with defensive coordinator experience, and Capers certainly fits that bill, having broken into the NFL coaching ranks in 1986. While McCarthy preferred a 3-4 defense, he said he didn't rule out staying with a 4-3.
"The 3-4 defense was the primary target, [but] I was still open to the 4-3," McCarthy said.
Other teams that may have considered Capers as a potential defensive coordinator included the Ravens, the Dallas Cowboys, the Jets and possibly the Kansas City Chiefs.
Chris Mortensen is a senior NFL analyst for ESPN. Information from The Associated Press was used in this report.