The Netherlands international completed his move to Turkey after falling out of favor at Inter, following his refusal to renegotiate his deal with the Nerazzurri.
The midfielder thrived under Mourinho before the departure of the Portuguese manager in 2010 and has struggled to produce the same level of performance since his exit.
"I called him before my decision because he's an important person in my career. I've asked his opinion and he gave me a really good advice," he told reporters at a press conference. "I've also spoken to Louis van Gaal. They both wanted me to go to Galatasaray so it was an easy decision.
"I had a great season in 2009-10 with Inter. We won everything. If you win everything, it's hard to win more. The last two years they had many coaches. We started to play with different systems and I started to play in different positions. It was a hard situation there after 2010."
There had been worries that the transfer may not go through given the length of time between a fee being agreed and Sneijder signing his contract, but the 28-year-old revealed he wanted to leave Inter on good terms before concluding the transfer.
"I had some problems with my ex-club Inter so I wanted to fix everything with them first. I had a good relationship with [Massimo] Moratti. I wanted to resolve everything with the club," he added.
The playmaker also revealed he had received other offers for his services, but is confident he has made the right choice in signing for what he described "a top club".