The New Zealander arrived at the Exiles in 2010 having previously played Super Rugby for the Highlanders and the Crusaders.
Comfortable at either 10 or inside centre, Bowden made an immediate impression at the club - going on to miss just one game last season.
The 25-year-old now seems set to complete a move to Leicester although he has so far refused to
Bowden wrote on Twitter: "Want to say big thanks to London Irish fans for their very passionate support. Just want to confirm I'll be leaving at the end of the season.
"It's a club with great people. Humbled to have captained side and to have won players player award. Winning remaining games all that matters.
"Looking forward to a new challenge, seeing some old faces and joining one of the best teams in Europe. Thanks."
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 Zealand All Blacks training jersey for 2013/14. Get in the Gear!
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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.