The former Game of Thrones actor stars as the lead character in Doctor Faustus at London's The Duke of York’s theatre.
In the avantgarde staging of the play, Kit, 29, shows plenty of his muscular body as he spends most of the play in his underwear, and also strips off for a shower scene that exposes his naked bottom.
However some audience members have captured his semi-nude scenes on their camera phones and shared them on social media.
One fan shared an image on Twitter alongside the caption: "Still haven't quite got over how intense 'Doctor Faustus' was! I would recommend (esp if you like Kit Harrington)," reports the Evening Standard newspaper.
When Harry Potter star Daniel Radcliffe starred in play Equus, leaked full frontal nude photos of the star were circulated online.
Kit's turn in the Christopher Marlowe play has been met with mixed reviews – but speaking at the gala night performance he told the Evening Standard: “I like to do work that seems very extraordinary and weird and whether they work or not at least they are trying to do something different.”
The play - which features a modern section by Colin Teevan - follows a man who sells his soul to the devil in order to be with the woman he loves.
The Times newspaper's theatre critic Ann Treneman gave the show a positive review, writing, "It's all wildly OTT (over the top) but I must admit I rather liked it."
Doctor Faustus runs at the Duke of York's theatre until 25 June (16).