Mafi arrived at Welford Road from Australia as an injury-dispensation signing in the summer of 2010 and has established himself as a stand-out performer with Tigers either as a second-rower or lock.
The Tonga international was a try-scorer in the Premiership semi-final and final in 2011/12 and man-of-the-match in Leicester's LV= Cup Final win. Mafi was also named Tigers Players' Player of the Year and the Supporters' Young Player of the Year.
Salvi, a former Australia 'A' cap, made his Tigers debut on the opening day of the 2011/12 season and has scored eight tries in 41 appearances as an openside flanker.
Leicester Tigers director of rugby Richard Cockerill is delighted that duo has decided to extend their stay at the club.
"Steve and Julian have become key members of our squad and firmly established themselves among the outstanding performers in the Aviva Premiership," he said.
"I'm delighted that they have agreed to stay and that they feel this is the best place to play their rugby.
"Steve is just 23 years of age and we believe he will get better and better in this environment, playing alongside other top-class players.
"Julian Salvi is an important player for us as an out-and-out openside. He's just 27 but he's an experienced player and has been in very good form with us."
Mafi and Salvi join England international duo Tom and Ben Youngs and Tigers second-row Graham Kitchener in agreeing terms to contracts beyond the end of the current season.
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.
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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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The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
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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.