Du Plessis impressed observers in the 2011 World Cup campaign, winning the man of the match award in the defeat to Wales.
The 27-year-old is equally at home in any of the back-row positions and has experience in England after a stint with Championship club Rotherham in 2009.
Wasps' director of rugby Dai Young said: "Everyone knows we have struggled for strength in depth in the back-row, with retirements and injuries making it very tough for us there.
"I was very impressed with Tinus at the World Cup and he brings the added bonus of versatility in a few positions so we will be a welcome addition for the rest of the season."
Du Plessis said: "It's been a dream of mine to play in the Premiership and to have joined a club with Wasps' rich history both domestically and on a European front makes it so much the better."
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.
$29.99
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
