While Twelvetrees was with the Lions, a coach there put him in touch with the-then Leicester Tigers academy manager, Andy Key, and after playing summer Sevens by way of a trial, he was taken on.

Focusing on his passing game to compliment his natural physicality was a big priority at this time which made him a huge asset in the midfield, where he was regularly deployed as a second playmaker.

[6] He made his first appearance for Leicester in the Heineken Cup on 11 October, filling in for Dan Hipkiss, who was ruled out just prior to kick-off.

In the opening games of the 2010–11 season, Leicester lost Toby Flood, Jeremy Staunton and George Ford to injury and Twelvetrees was again thrust into the starting line-up, this time at fly-half.

[15] A year later after leaving Leicester for Gloucester Twelvetrees was handed his first full international cap by Stuart Lancaster for England's Calcutta Cup clash with Scotland at Twickenham, scoring a try on his debut.

[16] On 12 June 2013, following an impressive performance against Argentina, Twelvetrees was called up to the British & Irish Lions tour of Australia due to concerns about possible injuries sustained by the fly halves and centres prior to the tests.

[17] On 19 July 2024, following his retirement, Twelvetrees returned to Gloucester as a backs and attack coach for Championship side Hartpury University.