The new partnership will end the Exiles's 20 years at their current home of Reading's Madejski Stadium and see them return to the Capital.
Championship side Brentford will have primary use of the new 17,250-capacity stadium on Lionel Road near Kew Bridge, which has also been confirmed as a host venue for the Women's European Championship in 2021.
Cliff Crown, Brentford FC Chairman, said: “We are building a high-quality stadium fully equipped and ready from day one for the rigours and demands of both Premier League football and Premiership rugby.
"Like us, London Irish has a long history in the area and prides itself on having strong roots in the local community. We look forward to continuing to work with them over the coming months to support their successful return to the capital.
“It was always planned that the stadium would host rugby and we have been working on ensuring we have a top-of-the range pitch so both sports can be played.
"We believe that the deal with London Irish is a good one for Brentford FC both in terms of the fit between our clubs and the financial contribution that will help us to strengthen our on-pitch performance.”
Irish, who are expected to win the Championship this season and return to the Premiership, had a contract to ground share with Reading until 2025-26, but a break clause was also inserted to allow them to leave early.
With falling attendances and a poor atmosphere in the 24,161 capacity stadium, Irish have been keen to move back to the heart of London.
London Irish Owner Mick Crossan said: “We’re delighted to be moving to the new Brentford Community Stadium with Brentford FC.
"It has been a long-held ambition to return to our roots in West London, and this stadium has everything we need – location, capacity and facilities – to re-establish ourselves as London’s authentic top-flight rugby club. We can’t wait to start playing there.”
Follow Sporting Life on social media - find us on Facebook here or tweet @SportingLifeFC
Related Rugby Union stories
