McCullough has been on trial at Rovers since the start of the summer, going on the club's pre-season trip to Portugual, and the defenderhas now signed a two-year contract with Paul Dickov's Sky Bet Championship newcomers.
The 19-year-old Northern Irishman told the club's official website: "I heard Doncaster were interested in taking a look at me so I came across and I've not looked back since, I've really enjoyed every minute that I have been here.
"Pre-season has been tough but as the manager has said it will give us a good base to build upon going into the season.
"The manager seems to have a good plan and wants the boys to keep improving.
"The rest of the lads have been very friendly and have made me feel very welcome - there's a good team spirit here."
- Sports & Recreation
- Paul Dickov