The Belgian, who notched 16 goals and 21 assists for PSV last term, completed a €9.5 million [£8.2m] switch from the Eredivisie side at the end of last month, and he is relishing the prospect of progressing his career in Italy.
"I chose Napoli with my heart," the 26-year-old said at his official unveiling.
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"I hope to be important because I haven’t come here to sit on the bench. I'm a player who can score and assist, even if I know I'll have to help out defensively too.
"The fans have already asked me to score against Juventus, evidently they don’t like them."
Mertens added that he would be willing to adapt his position to fit in with Benitez's plans at Stadio San Paolo next season.
"I hope to play on the left as I've spent the last five years there, but I’m ready to change if necessary."