The 22-year-old forward, who had scored 20 goals and provided 23 assists for Dutch side SC Heerenveen before joining Benfica last summer, has agreed a season-long loan deal and will link up with his new team-mates in Mainz on Thursday.
'He'll raise our level'
"Filip is a young player who has worked his way into a top European club with his performances," said Mainz's sporting director Christian Heidel. "We're delighted he sees the chance here to develop as a footballer. He's going to raise the level of our football further while his versatility gives our attacking play even more variety."
The 15-time Serbia international becomes the third new face in Mainz this summer after 05ers have already snapped up the 2014 FIFA World Cup participants Gonzalo Jara (Chile) and Stefanos Kapino (Greece).