The 22-year-old centre half has signed an 18-month deal with Rovers and is in line to make his debut in Saturday’s trip to MK Dons.
He said: “I’m delighted to be here. It was a massive opportunity for me that I could not turn down.
“I want to be playing and this is the perfect opportunity for me to be around a first team environment and get some games under my belt.
“I have experience of playing at Wembley where there were big expectations so there are opportunities that have really provided me with hunger.”
The Skipton born player came through the ranks at Burnley and signed a professional contract with the Clarets as an 18-year-old, though he did not make a senior appearance for his boyhood club.
He left in 2020 to join Sunderland and initially linked up with the Black Cats’ U23 group.
Younger made eight appearances in total for Sunderland, with just one coming in league action. He has been part of matchday squads this season but only been used in the Carabao Cup and Papa John’s Trophy.
Rovers boss Gary McSheffrey says the deal for Younger reminds him of when Joe Wright joined the club as a young defender packed with potential.
He said: "It was really important that we got a defender in, and when Ollie’s name was put to us we saw it as a good opportunity for the club.
“He’s got really good pedigree, he’s young and hungry which is the type of player we want here.
“He will be a good asset for the club and we feel he can be important for us in the short and long term.”
McSheffrey has been determined to add to his defensive ranks following the injury to skipper Tom Anderson, who is out for an indefinite period due to a plantar fascia issue in his foot.