London's Olympic Stadium will host its first rugby union match, when the Barbarians play Samoa in August.
The venue will host five Rugby World Cup matches later this year, and the game will be part of England Rugby 2015's testing programme.
Ireland's pool match with Italy, and the bronze medal play-off are among the World Cup games at the Olympic Stadium.
The Baa-Baas have already confirmed four other fixtures in 2015 to commemorate their 125th anniversary.
The Barbarians are a British-based invitational team, whose 2015 side will feature Australia's Berrick Barnes, New Zealand's George Whitelock and Argentina's Tomas Cubelli.
Barbarians' President Micky Steele-Bodger was delighted at the news, saying: "It is a significant honour for the Barbarians to take part in the first rugby match at the Olympic Stadium."
Samoa coach Stephen Betham was equally enthusiastic. "It is a great privilege for the Samoan Rugby Union to play the Barbarians in the run up to Rugby World Cup 2015," he said.
"Not only will it be our first match against the Baa-Baas, but at the Olympic Stadium too. It will certainly be a historical moment for us."