The agency won the business following a three-way pitch against two undisclosed agencies.
The process was handled by Yakult's marketing director, Alan Jelly.
The Japanese company, which has traditionally focused its advertising strategy on above-the-line channels, has appointed PAA to produce its first below-the-line campaign of note.
PAA will initially produce a customer relationship management campaign that will encourage people to make the probiotic drink part of their daily healthy-eating routine.
The move comes just three months after Yakult appointed Euro RSCG to handle its £5 million advertising account, following a three-way shootout against JWT and DDB.
Both Yakult and PAA were unavailable for comment.