On 21 April, Jennings played for NSW City Origin in their 18-12 loss. Jennings played in all 3 State of Origin games in 2013, scoring a solo try in Game 1 in the 14-6 win. On 6 October, Jennings played in the 2013 NRL Grand Final at centre with the Roosters being victorious over the Manly-Warringah Sea Eagles 26-18. Jennings scored to seal the victory with a spectacular try from a James Maloney grubber, beating two Manly players with his speed to ground the ball. Jennings was the Roosters highest tryscorer with 20 tries in 26 matches in an excellent year. After winning the premiership, he was named in the Kangaroos 24-man squad for the 2013 World Cup, scoring a try in his sole appearance against Fiji.