Flanker Mills has been with the Exiles since joining from the Scarlets in the summer of 2007, after a successful loan spell the previous season.
He has since racked up 141 appearances for Welsh, scoring 11 tries.
The Wales age-grade international led the club to promotion to the top flight last term, and is looking forward to the challenge of skippering the side in the Aviva Premiership.
"I love the club; I've been here so long that I feel part of the furniture," said Mills.
"London Welsh is very special to me and I've got a lot of very happy memories here.
"I've made friends for life and everyone has always been great to my wife and I, while on the rugby side it's great that we've taken the club to the Premiership."
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.
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.