Piutau agreed to join the Irish province this summer back in 2015 but didn't link-up with Les Kiss' side until this week.
The 24-year-old spent last season at English team Wasps after agreeing a short-term contract and he proved himself to be a revelation at home and abroad.
Piutau, capped 17 times by New Zealand, bagged six tries in 15 outings in the Premiership and was nominated for European Champions Cup Player of the Tournament shortlist after finishing with the most clean breaks (16) and metres gained (764) in the competition, scoring four tries in their run to the semi-final.
He took part in his first training session this week and spoke to Ulster's in-house TV channel about his start at the club.
"Training was pretty tough but it was good and I had fun with the guys," said Piutau, who can play in a number of positions in the backline.
"I am settling in well and the boys are making me feel welcome.
"Apart from the scratch on my head, it is going well. It is always good to put in hard work and go to those dark places with the guys."
He added: "Every pre-season is tough and I have not done one for a while but you get the hard work done now and then you benefit from it later in the season."
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