[4] He made his first-team debut on 18 October 2003, coming on as a last minute substitute for Iain Hume in a 2–1 win over Oldham Athletic at Prenton Park.
[9] Having been limited to only five appearances in the first half of the 2006–07 season under new boss Ronnie Moore, Jennings joined Graham Turner's Hereford United on loan in January 2007.
[10] He impressed at Edgar Street, which led to his loan being extended to the end of the 2006–07 season, and he played a total of 11 League Two games for the "Bulls".
Jennings re-established his place at Tranmere during the 2007–08 season, appearing in all but five league matches, usually partnering Paul McLaren in the centre of midfield.
[14] He signed a new one-year contract in May 2010, leaving manager Craig Brown to say that the deal was a "massive boost" for the club and that "he's an excellent midfield player who has been at the heart of everything we did in the second half of the season".
[15] The Association of British Bookmakers investigated "suspicious betting patterns" on a red card being shown to Jennings for dissent during a game in December 2010.
[19] After the police ended their investigation, Motherwell manager Stuart McCall criticised unnamed Scottish football officials who had suggested that Jennings should have been suspended while under suspicion.
Despite this, he was judged to be surplus to requirements at the Ricoh Arena by new boss Steven Pressley, and his contract was terminated by mutual consent in September 2013.
[29] He made a scoring start to his third spell at Prenton Park, netting from long range in a 2–2 draw with Stevenage on 1 November.
[37] Jennings signed with National League North club Southport in June 2017, and was described as a "massive coup" for the "Sandgrounders" by manager Alan Lewer.
[40] He helped Warrington to a third-place finish at the end of the 2017–18 season, which qualified them for the play-off semi-finals, where they were beaten 3–0 by Grantham Town.
[44][45] Speaking in February 2014, Tranmere Rovers coach John McMahon labelled Jennings a "fire blanket" for his ability to break up opposition play across the pitch.
[46] In September 2022, Jennings and Alan Rogers stood trial for allegedly blackmailing an unnamed football manager over gambling debts of nearly £1million.