In October 2011, Jennings played for the Australian Schoolboys. In 2012 and 2013, Jennings played for the Penrith Panthers' NYC team. On 20 April 2013, Jennings played for the New South Wales Under-20s team against the Queensland Under-20s team. On 6 October 2013, Jennings played in the Panthers' 42-30 win over the New Zealand Warriors in the 2013 NYC Grand Final. In 2014, Jennings moved to the Panthers' New South Wales Cup team. In February 2014, Jennings played in the Panthers' inaugural NRL Auckland Nines squad. He suffered a season ending elbow injury in the tournament. On 30 April 2014, Jennings re-signed with the Panthers on a 2-year contract. In Round 1 of the 2015 NRL season, Jennings made his NRL debut for the Panthers against the Canterbury-Bankstown Bulldogs. He scored a try on debut. In September 2016, Jennings signed a 1-year contract with the Parramatta Eels starting in 2017, after not receiving any game time in the 2016 NRL season. On 2 April 2018, Jennings made his debut for Parramatta in their 30-20 defeat by the Wests Tigers. On 28 August 2018, Jennings won the Jack Gibson NRL Coaches Award after being voted the club's best back. On 30 October 2018, Jennings signed a one year contract extension to remain at Parramatta until the end of the 2019 season. Jennings began the 2019 NRL season in reserve grade as coach Brad Arthur chose both Blake Ferguson and Maika Sivo as the club's first choice wingers. In Round 10, Jennings was called into the Parramatta side to cover for the suspended Sivo as the club travelled to Townsville to face North Queensland. With the scores locked at 10-10, Jennings attempted a pass across his own goal line to Ferguson on the first tackle. Ferguson lost the ball and North Queensland crossed over for the match winning try. The following week, Jennings kept his spot on the wing as Parramatta lost to last placed Penrith 16-10. Jennings was then subsequently demoted to reserve grade by Arthur. After being demoted, Jennings made no further appearances for Parramatta in the 2019 NRL season. Jennings instead played for the club's feeder side the Wentworthville Magpies in the Canterbury Cup NSW competition. Jennings scored a try in Wentworthville's 2019 grand final defeat against Newtown at the Western Sydney Stadium. In round 10 of the 2020 NRL season, Jennings was called into the Parramatta side as a replacement for the injured Blake Ferguson. In his first touch of the ball, Jennings knocked on which lead to a Manly try. In the final play of the game, Jennings scored a try but it was not enough as Parramatta lost the match 22-18 at Brookvale Oval.
