Garnett has been out of action for four and a half years due to injuries, Covid-19 and coaching commitments.
The 34-year-old was scheduled to return to the octagon back in 2019 for the Brave Combat Federation, though his plans were put on hold after suffering a broken jaw just six days before his fight with Rany Saadeh.
"That put me out for 2020," Garnett told Planet Sport. "Then obviously in 2021 and 2022 we were coming out of the pandemic.
"Then all that's been going on in the gym. I've got guys like [Muhammad] Mokaev. Got some other really world class talent coming through at the academy so feeling a bit diverted to that.
"Then 12 months ago, it was time to get back in the cage, but I couldn't get the right offers.
"I was speaking with promotions like the PFL and trying to get on some big shows, but they were saying I needed a fight and I didn't want to go back to a regional show.
"Then this fight in Paris just came to me. I think it was the right timing. It's been a little time out but I'm obviously full time in the sport, I'm a full-time coach, I've got a coaching degree, I've got my own academy, I've already coached fighters to the UFC from amateur."
Garnett admitted that due to his long period of inactivity, his focus ahead of the fight is on fitness.
He added: "I've been on the mat, so I've been developing technically and tactically. But probably where I've not put the time has been in my physiological development.
"I've been putting an emphasis on my fitness, strength and conditioning. The last few weeks, just trying to get that back up there. Obviously, that's a big aspect of performance. That's something I've been mindful of with my preparation.
"I think the Miguel Hago fight is a lovely fight to come back to. I'll be expecting a title fight on the back of that fight against some sort of elite European fighter."
Garnett and Haro will square off on January 22 at the historic Zenith arena in Paris. The event will be broadcast live on DAZN.