Jean de Villiers will arrive to Munster on Thursday and begin his contract subject to the regulatory medical and fitness examinations on his arrival in Ireland.
Munster coach Tony McGahan said: "Jean de Villiers is recognised as one of the top midfield rugby players in world rugby. I'm looking forward to having him in our squad. He brings a wealth of experience and a skill level that will benefit Munster on and off the field."
Rob Wagner, managing director of Western Province Rugby, said: "We are obviously sad to be losing Jean. As a captain and a player he has contributed significantly both on and off the pitch.
"Whilst we did everything in our power to retain his services, Jean has made up his mind to join the great Irish club Munster.
"We wish him all of the very best with Munster".