The news follows the extension of Alex Hunt’s deal into next year as the club look to continue in their efforts to ensure their brightest youngsters are nailed down.
Having featured in cup matches last season, Brennan spent time on loan at National League Notts County earlier this campaign and has impressed on his return, stepping in to cover injuries in the Wednesday defence.
Speaking on the announcement of his new contract, which will now run until 2024, Brennan said: “I’m really happy, I’ve broken through this season and I want to progress my career with Wednesday.
“The gaffer has told me how well he thinks I have done, he wants me to stay, and I feel I am really developing playing under him and obviously I want that development to continue.
“I’ve always had a good reception from the fans when I’ve been playing. I’ve received some really nice messages and it was always in my mind to stay with Wednesday, it’s home for me. This is the dream place to be so hopefully I can cement myself in the team and have a long career with Wednesday.
“I want to play as many games as I can, get as many minutes as I can, I’ve had a taste for it now and I’ve loved it.”
Owls boss Darren Moore has awarded Brennan with six League One appearances so far this season, a number that has enhanced his tally of 13 senior matches for the club.
Speaking earlier this month, Moore said: “Ciaran’s a youngster that we feel has the right potential and when called upon he’s stepped in and done really well.
“He’s another youngster that has parts of his game to develop and we will continue to develop them.
“He’s developing nicely, he’s got a lovely maturity about him for someone so young and we’ll keep working with him and make sure he’s doing the right type of work to see him get better.
“It’s great for him that he’s competing against some seniors in terms of where his performances have been of late.”