The procedural series is recognised by research houses as the most-watched drama series on television globally, having become the biggest scripted show in the US back in the 2009-2010 season.
Much of its success has been laid at the feet of lead Harmon, whose influence behind the camera has also increased. He has now signed on for two more seasons of the show, which CBS Studios International shops globally.
NCIS, which follows special agents at the Naval Criminal Investigative Service, is currently in its thirteenth season, having launched back in 2003.
The news is a boon for CBS Entertainment president Glenn Geller, who succeeded the long-serving Nina Tassler in September last year.