Van Niekerk has scored eight tries for his country so far

The date of the 27-year-old's arrival depends upon the announcement of South Africa's World Cup squad on 23 July.

"He will be a key part of squad in the next few years and brings experience and leadership," said Saints' director of rugby Jim Mallinder.

"His attitude to helping young players was key to the decision to sign him."

Van Niekerk captained the national schools, U19 and U21 sides before winning the first of his 46 caps for the Springboks.

So far his whole playing career has been spent in South Africa but he said the passion of the Saints fans was one of the things that had persuaded him to make the move to England.

"To come to a club that's as rich in tradition and history as Northampton is an awesome thing," he said.

"I could not believe the supporters when I came to watch the game, they were very passionate. I'm looking forward to it immensely."