The 20-year-old student, who caught the eye of Boro scouts while playing for Birmingham University and played for the club's development squad last season, has signed a two-year deal.
"I'm really looking forward to the challenge of professional football at Middlesbrough," says Christian, who hopes to continue his history studies at Teesside University.
"This is the opportunity I have always wanted. I've spoken briefly with Tony Mowbray and it's nice that he has shown some confidence in me.
"I'm looking forward to getting started next season and making the most of this chance."