The 24-year-old Irishman, who moved to Welford Road from Leinster in 2011, has scored seven tries in 26 appearances for Leicester, including two in last Saturday's league victory at London Irish.
Leicester director of rugby Richard Cockerill said of the wing/full-back: "Niall made a big decision to leave Ireland and come to Leicester last summer and he has been been a very important member of the squad here for the last two seasons.
"He has been improving the whole time with us. He is a good young player who is developing really well and doing a good job for us."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
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Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
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