The Scotland goalkeeper, 24, signed for the Bluebirds from Norwich on Wednesday and has already spoken of his desire to revive his international career under the guidance of Dave Jones.
And having penned a four-year deal, Marshall admits that once he saw Cardiff's set-up first-hand, he was only going to come to one decision.
He told the club's official website: "Things happened very quickly and the chance to join Cardiff was too good an opportunity to turn down, especially after I had seen the place.
"I have to say I have been very impressed, it all looks fantastic. I met the manager and the chairman along with Martyn Margetson at the new training ground and it is superb. I'm really pleased to have signed.
"The way the club is set up it's desperate to get to the next level and I'm looking forward to coming in, working hard and putting in performances to hopefully gain the number one spot. From there I hope to achieve what we will all be working towards and that's promotion."