Danaher succeeds prop Clarke Dermody as skipper.
The 32-year-old is the club's longest-serving player, having made 242 appearances during his time, scoring 21 tries.
During his 13 years with the Exiles, Danaher has become a real favourite amongst the London Irish supporters for his great passion and dedication for the only team he has ever played for.
In 2002, Danaher was part of the London Irish team that beat Northampton Saints in the Powergen Cup Final and it is experiences like this one he wants to share again with the current crop of players.
Declan said: "It is a huge honour for me to be named Club Captain for next season.
"I am following in the footsteps of Club greats in the likes of Clarke Dermody, Seilala Mapusua, Bob Casey, Mike Catt and Ryan Strudwick who were all exceptional leaders.
"When Brian Smith offered me this opportunity, I was delighted to accept. Having worked with Brian I know his drive and the success he is after. A few years ago, he managed to get a hell of a squad together which then went onto a Premiership Final so I am well aware of what he is capable of.
"London Irish means the world to me and I will endeavour to make sure that I don't let the boys or the London Irish family down. We have an exciting new squad; we are training hard and looking forward to facing Saracens in the London Double Header on September 1 at Twickenham."
Danaher will work with a senior leadership group. These leaders are Alex Corbisiero, David Paice, Bryn Evans, Tomás O'Leary, Ian Humphreys and Shane Geraghty.
All six players, along with Danaher, will take responsibility for their area of the game. Corbisiero and Paice will run the scrum, Evans the lineout, Danaher and O'Leary will organise defence, and Humphreys and Geraghty will control the attack. One of these leaders will also be the matchday captain.
London Irish director of rugby Brian Smith said: "I'm delighted that Declan has agreed to be club captain next year.
"He is a player who has come up through the ranks at London Irish and has been involved in Finals and Cup triumphs.
"He will bring experience and passion and be a fantastic influence around our squad this season.
"The leadership group will take responsibility for their specific elements of the game and one will captain the side on a matchday.
"All seven players are tremendous leaders and will set the standard for the squad this season."
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