Henderson has won 72 caps in green since his Test debut against South Africa in November 2012, becoming a key part of Andy Farrell's leadership group in recent years.
The 31-year-old, who has made 139 appearances to date for Ulster, was part of the 2023 Grand Slam-winning squad, adding to the Six Nations titles he won in 2014, 2015 and 2018.
Commenting on his contract extension, Henderson said: "I am delighted to sign with the IRFU and Ulster for another two seasons and look forward to continuing my journey in Ireland. It is an incredible honour pulling on my provincial and international colours and I believe that there is more to come as we look to build in the months ahead.”
IRFU Performance Director David Nucifora added: "Iain has developed into an important leader within both the Ireland and Ulster environments and we are delighted to have ensured that he continues his career in Ireland. I have no doubt that he will continue to add positively to both environments in the months and years to come.”
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