Sunday marked the 40th anniversary of ABBA's international breakthrough when they won the 1974 Eurovision Song Contest with the song Waterloo, one of several hits the choir performed.
The performance was staged outside a museum dedicated to the group that went on to sell an estimated 380 million albums. ABBA has not recorded together for three decades.
Andersson did not accompany the choir for Waterloo or Dancing Queen, but did play Thank You for the Music.
The museum courtyard was packed with people who sang along with the 50-strong choir formed to celebrate the anniversary of ABBA's Eurovision win in Brighton, England.
The choir performance was live streamed by Stockholm tabloid Aftonbladet.
At the museum, visitors can walk through the band's history and see videos, stage costumes and other memorabilia, and even perform virtually with ABBA.
ABBA's fanbase has been rejuvenated by the hit musical and film Mamma Mia, as well as music streaming technology which has made its music accessible to a younger generation.
A special photobook with over 600 photos has also gone on sale as part of the anniversary.
Former guitarist and songwriter Bjorn Ulvaeus, the main force beind the museum, has said it told the group's story as he envisaged.
The other members Anni-Frid Reuss (formerly Lyngstad), Andersson and Agnetha Faltskog have also endorsed the exhibit.
The museum is part of the Swedish Music Hall of Fame, which includes other displays recounting the history of Swedish popular music.
