The Montpellier Herault star joins compatriots Leonardo Senatore and Ignacio Mieres in signing a deal at Sixways for 2013-14.
"Agustin is a quality international who will add real strength in depth and power to the pack of forwards," head coach Richard Hill told the club's official website.
"I really like the way he plays the game and the clear ball carrying ability he possesses. He will help us continue to develop our attacking game and has played some lovely stuff at Montpellier this season.
"He speaks very good English, which is important, and is an experienced international player who will know Leonardo, so I am sure they play well together.
"We have signed a very passionate rugby player whose attitude and dedication is superb. I am sure he will be a big asset for the Warriors as we plan for the future."
Creevy, 27, has 22 caps for Argentina.