Jenkins is the second player with his name to have played competitive football for Watford. He is no relation to the Ross Jenkins who played for Watford from 1972 to 1983, and was a two-time Watford Player of the Season. During the 2007-2008 season he played regularly in the club"s under-18 side, as well as appearing for the reserves.
After appearing frequently for Watford"s first team during the 2008 pre-season, he made his competitive debut on 12 August 2008 whilst still an academy scholar.
Jenkins played the entire game as Watford beat League One side Bristol Rovers 1–0 in the League Cup. He remained in the club"s League Cup team, playing full games against Darlington, West Ham United and Swansea City before Watford bowed out to Tottenham Hotspur in the quarter-final.
Jenkins made his league debut in the defeat at Barnsley on 15 November 2008 under the management of Malky Mackay, and retained his place in the team thereafter, scoring his first league goal in the 3–2 defeat at promotion contenders Birmingham City on 6 December. He made his 50th start for Watford on 20 October 2009 against Ipswich Town.
Jenkins then went on to represent England at U20 level,playing at the Hawthornes against Montenegro beating them 5-0.
Jenkins signed for Plymouth Argyle on an initial one-month loan on 21 September. After scoring his first goal, Jenkins said he determinted to expect to score more goals at Plymouth. He scored his first goal for Barnet in a 3–2 defeat at Accrington Stanley on 16 March 2013.
Jenkins made 5 appearances in total before returning to Watford.
After leaving Watford, Jenkins started training with Malky Mackay"s Wigan Athletic at the beginning of the 2014/15 season. On 17 September 2015, he joined Crawley Town, having been without a club for more than a year.
Jenkins received his first call up to the England U20 squad on 7 August 2009. He started in their friendly against Montenegro a few days later at The Hawthorns which ended in a 5-0 victory.