He quickly settled in at Kingsholm, and his partnership with fly half Freddie Burns soon caught the eye of many observers, including England Head Coach Stuart Lancaster.
After making a try-scoring debut for England in the RBS Six Nations against Scotland in February 2013, Twelvetrees was called up to become Gloucester Rugby's first British and Irish Lion since Phil Vickery, when he joined up with the squad on the 2013 tour of Australia.
Meanwhile, his standing within the Gloucester Rugby squad was reflected by Director of Rugby Nigel Davies naming him vice captain for this season.
With his current deal set to expire at the end of this season, Davies has acted quickly to secure the services of one of England's brightest talents and a key part of his Gloucester side.
"It's really positive news from our perspective. Billy has made a huge impact in his time here. He's made a big impact on the team itself, but also, individually, he's made progress and become an England international and then a British Lion.
"It's great that we've extended his deal by another two seasons. He will be part of a core group of players that we keep together, moving forward over the next couple of seasons.
"What he brings to this team is huge. He's got great mental strength and huge belief. He's very physical as a player, has a lot more in him in terms of his rugby ability, and is very unique in that 12 position. He can take it up, play physically but also has some subtle touches, as well as being a kicker.
"It's a statement of where Gloucester's going. Billy wants to be part of this team moving forward. He loves Gloucester, loves this environment. He loves Kingsholm. He can see what our ambitions are. Billy's a winner, he wants to win things and wouldn't have signed if he didn't think that our ambitions matched his own."
Twelvetrees has rapidly become a fan favourite at Kingsholm and explained that committing his future to Gloucester was a simple decision.
"I'm really settled here. The club has been great to me, and this has seen me develop my game and ultimately earn international recognition.
"I've made great friends here and, to continue playing with the lads and developing partnerships, is something that I cannot wait to continue.
"We as players, speak a lot about how great the Gloucester fans are and, to play in front of the fine support we have as a club, is all you can ask for as a player.
"The team is still developing and the talent and potential here is great. So, I can't wait to see where we go and what we can achieve, and I couldn't imagine not being part of it!"