Halfback Pearce will combine with recalled Sydney Roosters team mate and five eighth Braith Anasta, replacing the injured Peter Wallace and Greg Bird among several changes from the team that lost Game 2 in Brisbane. Canberra's Monaghan replaces the injured Mark Gasnier in the centres.
Willie Mason has been pushed forward into the front row with Craig Fitzgibbon dropping back to the second row.
And prop Ben Cross returns from injury to claim a spot on the bench at the expense of Newcastle team mate Steve Simpson.
Fittler praised the selection of Pearce with Rooster's teammate Braith Anasta in the halves and says the two will bring the composure needed for NSW to win game three and claim the series title.
NSW team: Brett Stewart, Jarryd Hayne, Joel Monaghan, Matt Cooper, Anthony Quinn, Braith Anasta, Mitchell Pearce, Willie Mason, Danny Buderus (capt), Brett White, Craig Fitzgibbon, Ryan Hoffman, Paul Gallen Interchange: Kurt Gidley, Anthony Laffranchi, Ben Cross, Anthony Tupou.
Up north, Queensland have named an unchanged team for their must-win Origin III clash against NSW at Sydney on July 2.
Melbourne hooker Cameron Smith will again captain the team in the absence of inspirational Broncos pivot Darren Lockyer.
The squad is the same as the Maroons team which kept their series hopes alive with a record equalling 30-0 Origin II win over NSW at Suncorp Stadium.
Queensland face a tough task at Sydney's ANZ Stadium where they have won just one match and drawn another in 13 games.
QLD team: Karmichael Hunt, Darius Boyd, Greg Inglis, Brent Tate, Israel Folau, Johnathan Thurston, Scott Prince, Steve Price, Cameron Smith (capt), Petero Civoniceva, Michael Crocker, Ashley Harrison, Dallas Johnston Interchange: Billy Slater, Ben Hannant, Nate Myles, Sam Thaiday.
In other news, Tony Archer has been retained as referee for the State of Origin rugby league series decider despite criticism from the losers in the first two matches.
Queensland referee Mal Meninga repeatedly slated Archer's performance after the first game at Sydney's ANZ Stadium on May 21, claiming he did not police the ruck area strictly enough as the Blues won 18-10.
And the Blues were adamant Archer went too far the other way with a rash of penalties in game two when the Maroons triumphed 30-0 at home at Suncorp Stadium.
However, Archer has retained the confidence of the Australian Rugby League which has put him in charge of game three at ANZ stadium on Wednesday week. Archer will be assisted by sideline officials Russell Turner and Steve Chiddy with Bill Harrigan and Tim Mander as the video referees.