Career
He has previously played for Nottingham Forest, Brighton & Hove Albion, Cheltenham Town, Hibernian and Buxton. His career has been disrupted by a medial knee ligament injury. He made his League debut five days later, coming on as a second-half substitute for Kris Commons.
On 12 January 2008, the youngster came on as a late substitute against Leyton Orient to score his first professional goal for The Reds, the last of Forest"s goals in a 4–0 victory.
Thornhill started his first Forest game when he stepped in at the last minute to replace Chris Cohen in the heart of midfield. He has since been battling for a midfield spot, scoring his second goal of the season in a 1–1 draw at Southend.
He helped The Reds finish second in the 2007-2008 season in League One, gaining promotion to the Championship. With The Reds gaining promotion, manager Colin Calderwood commented that Thornhill would be given the chance to impress the following season.
On 21 July 2009, Thornhill joined League One side Brighton & Hove Albion on loan as part of the transfer deal which saw Joel Lynch join Nottingham Forest.
After making seven appearances for Brighton, Thornhill returned to Nottingham Forest in December. Thornhill then joined League Two side Cheltenham Town on a one-month loan deal in January 2010. On 21 January 2011, Thornhill agreed a deal to sign for Scottish Premier League club Hibernian, subject to a medical.
Hibernian confirmed the transfer a few days later.
His 2010-2011 season was ended prematurely by a medial knee ligament injury. Thornhill was released from his contract in January 2012.
He had made just 15 appearances for Hibs in his year with the club Thornhill signed for Northern Premier League club Buxton in November 2012.
He signed for Shaw Lane Aquaforce, then of the Northern Counties East Football League, in July 2014.