The lock put pen to paper on an extension with the Irish Rugby Football Union until June 2021.
Ireland captain Best and full-back Kearney earlier signed new IRFU deals that will expire after the World Cup next year.
Henderson returned to the Ireland side for a victory over England at Twickenham on Saturday which sealed the Grand Slam and now has another reason to celebrate.
"I am delighted and extremely proud to extend my playing career in Ireland for a further three years," he said. "The Irish rugby set-up is one of the best in world rugby and, since turning professional, I have been able to develop in an environment that has seen both provincial and national teams being part of some fantastic days and indeed some challenging times over the past seasons.
"I am extremely confident that, with both Ulster and Ireland, we will continue to meet those challenges head on.
"There is currently some exciting talent throughout Ulster and Irish rugby and it is my ambition to continue to push for further honours at both provincial and national levels."