The 22-year-old defender spent the previous season on loan at Championship outfit Yeovil Town, and has made just five top-flight appearances for the Goodison Park club in his fledgling career.
Duffy was an unused substitute for Republic of Ireland in their 2-1 friendly defeat to Turkey on Sunday, and is yet to earn a senior cap, but first the centre-back is concentrating on making an impact at Everton.
"Roberto (Everton manager Martinez) told me that pre-season was my chance to shine and he's said to me that if I am where he thinks I am - from what he's seen of me this season - then I'm going to be involved," he told the club's official website.
"And if I'm not, we'll see at the end of pre-season what we're going to do. It's a big summer for me, it's up to me.
"Seeing Seamus (Coleman) progress is brilliant for me because he's such a hard worker and it's a reward for how he lives.
"And he's very good to me, he says, 'If I can do it, you can do it', so we'll see what happens."
