The 24-year-old had been linked with a move to London Irish or France after a frustrating season due to injuries - with initial contract talks having stalled.
But he has now decided to remain with the Heineken Cup winners for at least one more year, although he is not expected to play until after Christmas following neck surgery.
"We are delighted that Luke has committed to the province for another year," said Leinster coach Joe Schmidt.
"Luke is an outstanding talent and he has played a major role in Leinster's recent success."
Fitzgerald toured South Africa with the Lions in 2009 and has made 23 appearances for Ireland.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
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The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.