Leinster reserve scrum-half Brian O'Riordan will move to Guinness Premiership club Bristol in the summer.
Bristol coach Richard Hill said: "I've been looking for someone who can provide genuine first class cover for Shaun Perry as we think that Shaun will be involved with the full England set up at times over the next year or so," said Hill.
"We need somone who can step and perform at the highest level and Brian meets that criteria.
"At the same time we didn't need an individual who would come in and demand a first team place without earning it. We've spent time with Shaun and developed him and he is our number one.
"Brian's 25 and just the right age for us to be able to work with him on his skills and really help him to develop his game.
"He's been over to Bristol a few times and we've worked on his skills and his technical training and he's proved to be very receptive to new ideas.
"He's similar to Shaun physically. He's 6ft 1" and powerful. He'll attack the fringes and he's quick enough to go through a gap. He's also a few years younger than Shaun so we're taking a long term view with regard to his development."