Sportal.co.nz 18.Apr.2013Getty Images
Mitchell, 29, has signed a two-year deal with the star-studded French Top 14 side and will link up some of the world's top rugby players, including former England five-eighth Jonny Wilkinson and France's Frederic Michalak.
Mitchell says he consulted several players before making his decision, one of them being Giteau.
"I know him (Giteau) pretty well - I was his best man," Mitchell said on Wednesday.
"Knowing that when I get there, there will be a level of comfort as well - being in a foreign country, but having someone there that I can have some comfort around."
He also spoke to South African winger Bryan Habana, who is joining Toulon at the same time as Mitchell.
"Bryan is in a similar position to me - he's represented his country for many years now, he's achieved a lot and he feels as well that it's time for him to challenge himself in a different environment," Mitchell said.
"I guess in that regard we're probably somewhat similar."
Mitchell said it was a tough decision to make, but dismissed suggestions it had something to do with being left out of this week's Wallabies logistics camp.
"Robbie (Deans) made it very clear to me as to the reasons why I was left out of that squad the other day and by no means does that mean there's no way for me to work my way into the squad over the next six weeks or so," Mitchell said.
"I certainly don't want this to be seen as me turning my back on the Wallabies or the Waratahs because playing for Australia means absolutely everything to me.
"I just feel it's the right time for me. I think it's a great opportunity to experience a different culture and a different environment."
Mitchell has been named in the Waratahs' starting line-up to play the Chiefs at Allianz Stadium on Friday night.