The 25-year-old Northern Irishman has been handed the difficult task of filling in for world champion Casey Stoner, who is recuperating in Australia after undergoing surgery on the ankle injuries he sustained in a qualifying crash at Indianapolis.
Rea will combine racing in motorcycling's premier class with his duties with Honda in the Superbike World Championship, where he currently lies fifth in the standings.
Rea has been able to rack up the miles over three days of testing, but stepping up into the rarefied atmosphere of grand prix racing will nonetheless be a tough adjustment.
The Briton knows it will take him time to adapt, but cannot wait to get started at a track where he has tasted success in Superbikes.
He said: "For me it's a big dream come true just to race in MotoGP.
"It's been very unfortunate for Casey to sustain such an injury when he was having a very strong season and my best wishes go to him while he recovers.
"Now my job is to replace him and I will try to do the best I can.
"I love Misano, I've already raced there this year and I finished second, it's also where I had my first ever Superbike win in 2009 and I enjoy the circuit and the Italian fans, they are always very enthusiastic.
"I take this opportunity like a great gift from Honda. In the few days I've spent with the team I have felt very good, they understand it will take me some time to push with this bike but I'm learning every time I get on it.
"It's been great to have these three days testing on the bike to prepare myself and for sure Friday morning will be less chaotic.
"We already have the riding position set, the base set-up is set and I understand the electronics a little more. I know it's going to be busy, but I'm ready."
Rea will also be looking to try and help team-mate Dani Pedrosa's title bid.
The Spaniard has won the last two rounds in Indianapolis and Brno to close to within 13 points of Yamaha's Jorge Lorenzo at the top of the standings.
There will be an added poignancy to this weekend's racing as this will be the first time the MotoGP paddock has raced at Misano since the track was named the 'Marco Simoncelli circuit', in memory of the Italian rider who lost his life at Sepang last year.