The 31-year-old fractured his shoulder in the quarter-final defeat of Argentina at Eden Park last night and was ruled out for the rest of the tournament by team doctor Deb Robinson.
"From today onwards, I will be a former All Black," Muliaina said, with tears in his eyes.
"It only sunk in that it was over about five minutes ago.
"I really wanted to have a finish in a couple of weeks' time but it is not to be. This is rugby. Last night I was on top of the world but it is like a roller coaster.
"Bitter disappointment... but I am particularly proud to be an All Black. I have enjoyed my time and met some amazing people," he added. "And I am proud to be a Kiwi and proud to be an All Black."
Muliaina said he had known straight away that something serious had happened and that although it was an intense disappointment, his milestone appearance went some small way to ease the pain.
"I can be called a hundy (100) now instead of a 99," he smiled to a group of reporters in a central Auckland hotel.
"New Zealanders have been right behind me all the way so it has been fantastic.
"Today is about reflecting on what I have done... and spending time with my family.
"The biggest thing I'll miss is the people. I've spent almost a third of my life here and it has been outstanding
"What other job can you go to where people get out of their seats and cheer you? Or criticize you? I am just so proud and grateful for all the opportunities."
Muliaina said he would switch instantly from All Black stalwart to All Black fan.
"My job now is to be an outstanding spectator and get behind these guys. It (playing) is over."
"I haven't seen the boys too much this morning. Don't know if I am quite an armchair critic yet, but hopefully they can go well this weekend.
New Zealand face Australia in the second semi-final next weekend, while France take on Wales in the first.
"It's all been great and I will miss a heck of a lot... nice to have known you guys as well," he told reporters, before leaving to a round of applause.