He came through the Leinster Academy before moving to England where he spent two seasons with the Exeter Chiefs. In 2012 he joined the Brumbies in Australia for whom he has made 20 appearances so far.
Murphy will link up with Ulster in August at the end of the current Super Rugby season.
Commenting on his move back to Ireland, Murphy said: "When I was deciding my future, it came down to joining Ulster or staying with the Brumbies.
"The Brumbies are a fantastic franchise and Canberra is a brilliant place to live, but I am Irish, I have an Irish family and I have always had the urge to return to Ireland one day and to play my rugby back home.
"Ulster are a quality team. They are currently one of the leading sides in Europe and their fans are famous around the world.
"It is an exciting time to be joining the province with the new stadium and the new training facilities that have been built at Ravenhill.
"I spoke to David Humphreys about the vision that he has for Ulster - he has huge ambition and big aims for the team. That is exciting and I hope that I can play a part in bringing those aims to reality."
Ulster's director of rugby David Humphreys added: "Ruaidhri is a highly talented young Irish prop whose experience of Super Rugby will bring an extra dimension to our front row next season.
"I am delighted that he is joining us and I have no doubt that he will be a huge success at Ravenhill in the coming years."