A former youth player with Watford, Jennings made his professional debut for the Hornets on 10 April 1970, a third place play-off game against Manchester United in the 1969–70 FA Cup campaign at Highbury which the team lost 2–0.
[8] Jennings scored on his Hammers debut on 7 September 1974, against Sheffield United, and was a member of the FA Cup winning team of 1974–75.
[1][9] In 1977, Jennings spent three months on loan at NASL club Chicago Sting, playing with fellow Englishman Ronnie Moore and Scot Willie Morgan.
Although he retired after two substitute appearances for the Hatters, he later played for Isthmian League clubs Dagenham, Bishop's Stortford and Heybridge Swifts.
[1][3] Jennings later worked as a football agent, running the Premier Management agency, whose clients included former West Ham players Hayden Mullins and Kevin Nolan.