King made his National Rugby League debut from the bench for the Northern Eagles in a 42–14 loss to the Brisbane Broncos at the NorthPower Stadium in Gosford on 1 September in Round 26 of the 2001 NRL season.
[3] Manly, with Jason King forming a strong front row rotation with test forward Brent Kite and former Newcastle Knights prop Josh Perry, maintained their form in the 2008 NRL season and the Grand Final would again see the Sea Eagles come up against Melbourne.
This time however Manly-Warringah were in superlative form after easily accounting for St. George Illawarra and New Zealand Warriors in the Qualifying and Preliminary Finals.
[4] Despite playing on the bench in the Grand Final win over Melbourne, King was later voted Rugby League Players Association clubman of the year[5] King then went on to play in the front row in Manly's 28–20 win in the 2009 World Club Challenge over Super League champions the Leeds Rhinos at the Elland Road stadium in Leeds, England.
[citation needed] On 15 May 2011, King was named in the New South Wales Origin team for game 1 of the 2011 series at Suncorp Stadium in Brisbane where Queensland defeated the Blues 16–12.
An injury interrupted 2013 season saw him play only four games and miss Manly's 26-18 2013 NRL Grand Final loss to the Sydney Roosters.