Published Monday, 18 June 2012
O’Connor in action for Ulster in 2008. (© Getty)
The club says the pair will add significant depth to the squad for the 2012/13 season.
O'Connor returns to the province having enjoyed a one year spell with Connacht.
The 24-year-old established himself as the first choice flyhalf in Galway and produced a number of fine displays throughout the season, with one highlight being a 9-8 win over Harlequins in which he kicked all the team's points.
"I got a fair bit of game time down there and I'd like to thank Eric and his staff for that," said O'Connor.
"I gained more experience and feel I have improved as a player over the past season. But when the possibility arose to move back up to my home club, I thought it was a fantastic opportunity as Ulster is one of the best sides in Europe."
South African hooker Rob Herring will arrive in Belfast from Western Province.
The 22-year-old was involved in their Vodacom Cup squad there and has also enjoyed a brief stint with London Irish.
Ulster Director of Rugby, David Humphreys, has welcomed the signings.
"We are continuing to build our squad depth and the additions of Niall and Rob will further enhance our ability to compete over the course of a gruelling season," he said.
"Niall went away and gained a year's experience playing with Connacht and he has now come back to challenge Paddy and Ruan for the number 10 jersey.
"Rob is a typical South African forward who is very physical and is an accurate set piece operator. He is Irish-qualified and is a very ambitious individual who will thrive in our training environment."