The result comes as no surprise considering Williamson was seen bowling with a drastically altered action in Mount Maunganui last month during preparations for the national side's tour of the UAE.
Williamson was relieved to have put the five-month process behind him.
"It's a good feeling to be cleared, there's been a lot of work put in to correct the action so it's nice to pass the test," he said.
"It's one of those things that when you have it taken away from you, you want it a bit more and when you have it, you take it for granted a little bit."
The clearance is hugely significant for the Black Caps, who had used Williamson's dual talents to gain better balance with bat and ball.
The decision to play spinners Daniel Vettori, Ish Sodhi and Mark Craig in the third test against Pakistan - though it helped produce an outstanding test win - was likely forced by Williamson's unavailability with the ball.
And while his statistics do not make great reading - he has taken 24 test wickets at an average of 40.66, 23 wickets at 30.91 in 54 ODIs and three T20 wickets at 37 - he has often been asked to bowl in holding situations and has shown a knack for picking up important wickets.
A failure to have the ban overturned would have brought disaster, with an unsuccessful outing to have begun a year-long ban and thrown the planning for next year's 2015 ICC Cricket World Cup on home soil into disarray.
Williamson credited working with coaches for English county side Yorkshire and guidance from New Zealand spin coach Paul Wiseman with helping him make the change.
"It was a good process to go through and I think a good initiative from the ICC. I've enjoyed working on my bowling, it's something I haven't done a lot on in the past, that's probably why my action lost itself a little bit."
He was not sure when he would bowl in a match situation but added it was important for him to grow accustomed to bowling in pressure situations.
