Sean Reidy has signed a short term deal with the province after impressing with Counties Manukau Steelers in New Zealand.
The 25-year-old can play across the back row and is Irish-qualified through his grandfather who hailed from Castlegregory, County Kerry.
The additions will give Ulster even more depth in an already strong area. The province currently have three back row players on tour with Ireland in Argentina, while Roger Wilson played for a World XV against South Africa last weekend and they also have Nick Williams on the books.
And with young indigenous talent like Conor Joyce emerging too, it will provide the coaches with plenty of options for next season.
Butterworth, who played for the Ireland Club XV this year, is delighted to have signed his first professional contract, stating: "I can't wait to get started, it will be brilliant to be involved. Ulster are one of the best teams in Europe, if not the world, at the moment and it was a 'no-brainer' once David Humphreys offered me the contract.
"When I got the chance to go up and have a look at the facilities I was just really blown away. It's a top class stadium - everything is state of the art and I can't wait to start training."
Reidy is also relishing the prospect of joining the Ulster squad for their pre-season regime, admitting: "I had heard a lot about Ulster before I signed. They are a team with a lot of history and tradition but have done really well in their competitions recently and are a team on the up.
"It's a great opportunity for me to go over and learn from the coaches and try to develop my game."