The Welshman was sacked last month after the west Londoners failed to win any of their opening 12 league matches, with a 3-1 home defeat to fellow strugglers Southampton proving the final straw.
Redknapp was quickly installed as Hughes' successor, with the Rs boss revealing he had been just hours away from taking control of the Ukraine national team.
That option appears to have forced Fernandes' hand, with the QPR chairman revealing he could not risk losing out on the former Tottenham boss.
"Harry is a special manager," he told the club's official website.
"If he wasn't available, I would probably have persevered with Mark, but Harry is a fantastic manager.
"I've known him for years going back to when he was at West Ham. Harry being available swung it for us."
He added: "We're all in this together. No shirking. Let's see what Harry and the boys do.
"It's up to the 11 guys on the pitch to make it happen for us now. If we can pick up a couple of more wins before the new year, we're back to where we were this time last year.
"Coming off a win and three draws, there's a bit of renewed confidence about the place now."