He turned professional at Bristol Rovers, and made his first team debut in January 2006. He played in the 2007 Football League Trophy final defeat and was an unused substitute in the League Two play-off final victory, before becoming a first team regular from the 2007–08 season. He was sold on to Sheffield Wednesday for £50,000 in August 2011, and was a key first team player as the "Owls" won promotion to the Championship at the end of the 2011–12 campaign. However, he lost his first team place the following season, and was loaned out to Milton Keynes Dons in January 2013. He signed with Port Vale in July 2013. A key first team player in the 2013–14 season, he lost his first team place and returned to Bristol Rovers on loan in March 2015, helping Rovers to win promotion out of the Conference Premier via the play-offs before rejoining Rovers on a permanent basis in the summer. He helped Rovers to achieve a second successive promotion in the 2015–16 campaign.
Born in Bristol, Lines spent a year playing for Bitton as a 16-year-old, before graduating through the Bristol Rovers-backed Bristol Academy of Sport at South Gloucestershire and Stroud College. He had previously been released from the Bristol Rovers youth programme, but was re-signed at the age of 16.
He made his first team debut for Rovers on 21 January 2006, playing the last five minutes of a 2–1 win over Chester City at the Memorial Stadium. After two further substitute appearances in League Two, he made his first league start on 6 May, in a 3–2 home defeat to Macclesfield Town.
After three appearances in the 2006–07 campaign, he featured in six matches from March onwards, and was an extra-time substitute for Lewis Haldane in the Football League Trophy final defeat to Doncaster Rovers at the Millennium Stadium. He was an unused substitute in the League Two play-off final, as the "Pirates" won promotion with a 3–1 victory over Shrewsbury Town at Wembley.
He became a first team regular under manager Paul Trollope in the 2007–08 season, playing 27 League One games and featuring in eight of the "Gasheads" nine FA Cup games en route to the quarter-finals. He put in an "excellent" performance as Rovers beat Premier League Fulham on penalties in the Third Round on 22 January, and was fouled by Dejan Stefanović in an incident which saw the Serbian sent off. He scored his first goal in competitive football on 29 December, heading in the first goal of a 3–0 home win over Carlisle United.