The Hurricanes loose forward, who has played 20 Tests for New Zealand, played club rugby in Wellington on Saturday under the watchful eye of All Blacks forwards coach Steve Hansen and was given the nod as Richie McCaw's replacement ahead of young New Zealand Maori duo Tanerau Latimer and Liam Messam.
Henry said Masoe's experience had been the deciding factor but whether or not he would start in the opening Tri-Nations Test in Wellington on Saturday had yet to be decided.
"We have brought him in because he has experience in the All Blacks squad and he has been with us for some time and he knows the systems," said Henry.
"He has played against South Africa a number of times before and played well so he will adjust pretty quickly to that situation.
"Who will start in the loose forwards hasn't been decided yet we will discuss that when we have our selectors meeting and that will be announced on Tuesday."
Henry said the loose forward mix would be re-assessed ahead of the July 26 match against Australia in Auckland, meaning Masoe's long-term involvement in the squad is not guaranteed.
"We may want to take a different approach against Australia," he added. "We'll look at form and fitness and the team's plan again in a couple of weeks."
The New Zealand coach also confirmed Hurricanes skipper Rodney So'oialo would captain the All Blacks in the absence of McCaw.
So'oialo took over the duties when McCaw was forced from the field during the second Test against England with an ankle injury that will rule him out for at least six weeks.
"Rodney leads with actions more than words," said Henry. "He has the respect of everyone in the team and plenty of experience as captain of the Hurricanes."
Lock Kevin O'Neill has also been brought into the squad as cover for Ali Williams. Henry however, was confident Williams would be fit to face South Africa at Westpac Stadium on Saturday.
"I have spoken to him a couple of times during the week and Steve Hansen has spoken to him as well and the glass is one-and-a-half times full which is great, which is always Ali's attitude, so he's pretty upbeat," added Henry.
"But I guess when we start scrummaging and really going through the physical needs of the week, how he responds to that will be interesting. But I'm confident he will be fine."