Meanwhile, Benitez, who has submitted his application for UK entry clearance and completed all his required immigration documentation, is well above the required level to obtain a work permit having played in 86% of Ecuador's competitive games over two years.
"I am looking forward to playing for the Blues," he added on the club website.
"I will be giving everything to score as many goals as possible and share good times with this club."
McLeish hailed his arrival, saying: "Christian is a tremendous prospect who has lit up the South American international scene.
"The signing is really exciting for everyone at the club and I'm really looking forward to working with him. I look forward to seeing him in a Blues jersey.
The board deserve credit for the ongoing investment in the playing staff
Birmingham boss Alex McLeish
Birmingham's players return to training this week after the summer break and it is believed Benitez will join up with the first-team squad shortly, along with prospective new arrival Bowyer.
The former England midfielder has long been a target of McLeish's - and the Scot has heaped praise on his board for their support.
Benitez joins Stephen Carr, Scott Dann, Roger Johnson, Joe Hart - a season-long loanee from Manchester City - and Giovanny Espinoza in signing on the dotted line.
And with Bowyer expected to join soon and Newcastle midfielder Joey Barton also linked with a move to St Andrew's, McLeish said: "The board deserve credit for the ongoing investment in the playing staff and have pledged further support to strengthen our challenge.
"I have several names in mind for the crucial midfield positions. I know what I'm looking for in the team and the board have pledged their support to back me in this."
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