The 20-year-old, who is expected to start against Macclesfield in the FA Cup this weekend, broke into the first team earlier this season after an injury to Ben Turner.
The Welshman made the most of his opportunity, scoring a goal and impressing manager Malky Mackay in his three appearances in November.
"He's a kid that has a fantastic attitude and I think that's a great starting point," Mackay told the club's official website.
"He's someone that desperately wants to do well and learn, so I'm delighted for him. He's come in and managed to stand the test of playing in the first team.
"As a youngster you don't know whether they'll sink or swim until they play their first game at a professional level, but he took that in his stride. I've seen a lot of young centre-backs coming through and he's certainly one who has a lot of the correct attributes to go and have a good career."