Mourinho, who returned to Stamford Bridge in the summer, is the fourth manager that the centre-back has played under for the Blues following his arrival from Bolton Wanderers last year.
Despite the high turnover of coaches during his time in West London, Cahill is confident that the Portuguese will remain at the club for a long time.
"I was looking forward to that when Jose took the job because you knew a manager of his calibre was not coming for just a couple of months and going off," he told the Evening Standard. "He's here for a good while. That position is solid and settled now.
"Although we always try and concentrate on our job no matter what, it's great to know he's going to be the manager for the next few years.
"It's providing a more relaxed environment but it's not just about that. When a new manager comes in, it can bring a positive reaction, everyone is on a level playing field but everything changes."
Chelsea travel to Sunderland in the Premier League tonight.