Benny Andersson was born to 34-year-old constructional engineer Gösta Andersson and his 26-year-old wife Laila. His sister Eva-Lis Andersson followed in 1948. His musical background comes from his father and grandfather; they both enjoyed playing the accordion, and at six, Benny got his own. Father Gösta and grandfather Efraim taught him Swedish folk music, traditional music, and the odd schlager. Benny recalls the first records he bought were "Du Bist Musik" by Italian schlager singer Caterina Valente and Elvis Presley's rendition of "Jailhouse Rock"; this smorgasbord of different kinds of music was to influence and follow him through the years. When Benny was ten he got his own piano, and taught himself to play. He left school aged 15 and began to perform at youth clubs. This is when he met his first girlfriend Christina Grönvall. Benny got engaged to Christina after she became pregnant by him when he was just 15 years old. In 1963 they had a son, Peter Grönvall (In the 80/90’s Peter formed Sound Of Music and hit many hits in Sweden and then One More Time, a group that enjoyed European success with their hit "Highland" and later as Sweden's entry to the Eurovision Song Contest 1996.)

In early 1964, Benny and Christina joined a group with the odd name "Elverkets Spelmanslag" ("The Electricity Board Folk Music Group"), who by no means was a folk music ensemble: the name was a punning reference to their electric instruments. The repertoire was mainly instrumentals, and Benny recalls one of his standout numbers was "Baby Elephant Walk". In March 1964, "Elverket Spelmanslag" was up against another band in a talent contest, The Hep Stars. When Benny stepped in as the Hep Stars' keyboardist in October of that year, he knew this was what he wanted to do.  The Hep Stars got their breakthrough in March 1965 with their massive hit "Cadillac", eventually becoming the most celebrated of the Swedish 1960s pop bands. Benny consolidated his place as the band's keyboardist and musical driving force as well as a teen idol. The band performed mostly covers of international hits, but Benny soon started writing his own material, and gave the band the classic hits "No Response", "Sunny Girl", "Wedding", "Consolation", "It's Nice To Be Back" and "She Will Love You" amongst others. Benny and Christina had a daughter, Helene In 1965. They split in 1966 and never married. Christina kept custody of the children as Benny was currently at the peak of his Hep Stars' success. Benny met Björn Ulvaeus in June 1966, and the two started writing songs together, their first being "Isn't It Easy To Say", eventually recorded by The Hep Stars. He also had a fruitful song writing collaboration with Lasse Berghagen, with whom he wrote several songs and submitted "Hej, Clown" for the 1969 Melodifestivalen - the Swedish Eurovision Song Festival finals. The song finished in second place. During this contest he met vocalist Anni-Frid Lyngstad, and they soon became a couple. Around the same time his song writing companion Bjorn Ulvaeus met vocalist Agnetha Fältskog. The personal relationships and their song writing collaboration has led quite naturally to the very close co-operation which the four friends had during the following years. Benny and Björn scored their first hits as songwriters in the spring of 1969: "Ljuva Sextiotal" (a hit with Brita Borg) and "Speleman" (a hit for The Hep Stars). As the two couples began supporting each other during recording sessions, the sound of the girls' voices convinced the songwriters to try something together.  Thus, ABBA came to life. Benny Andersson has written music to several films for screen and television; the first attempt in the early 1970s for the obscure Swedish movie The Seduction Of Inga: the film flopped, but the 'Björn & Benny' single "She's My Kind Of Girl" surprised the composers by being released in Japan and becoming a Top 10 hit (the song re-named in Japan as "The Little Girl Of The Cold Wind"). During the next eight years, Benny & Björn wrote music to and produced eight studio albums for ABBA. Benny was engaged to Frida for about nine years. They married in October 1978 but divorced in 1981. He married Swedish TV presenter Mona Nörklit in November 1981, and had a son, Ludvig (born January 1982). Ludvig has since followed in his father's footsteps in forming his own band, Ella Rouge, and released a successful solo album in Sweden. After ABBA broke up in 1983, Benny continued writing music with Bjorn. Their first project was the musical “Chess”, written with Tim Rice. The "Chess" concept album - with vocals by Elaine Paige, Barbara Dickson, Murray Head and Swedes Tommy Körberg and Björn Skiffs - was released in October 1984, selling two million copies worldwide. The Paige/Dickson duet "I Know Him So Well" became a major #1 hit, and Murray Head's "One Night in Bangkok" gave them an Australian #1 and a US #3 hit. 'Chess' was staged in London's West End Prince Edward Theatre in May 1986, and ran for almost three years. A Broadway staging in April 1988 received disastrous reviews, and closed after just two months. In 1985, Benny and Bjorn wrote, produced and released an album with brother and sister Anders and Karin Glenmark, featuring new songs by Andersson/Ulvaeus. The duo named themselves Gemini, and a second album with more music by Björn and Benny was released in April 1987, containing the big hit "Mio My Mio In 1987, Benny wrote music and co-produced the soundtrack with Anders Eljas for the film Mio in the Land of Faraway, based on Swedish author Astrid Lindgrens Mio, my Mio. The title song became a huge hit in Sweden for Gemini. In 1987, Benny released his first solo album "Klinga Mina Klockor" ('Chime, My Bells'). All the music was written by and performed by himself on accordion, backed by the Orsa Spelmän (Orsa Folk Musicians) on fiddles. A second solo album followed in 1989 called: “November 1989.” In 1990, he scored a Swedish #1 hit with "Lassie", sung by female cabaret group, the Ainbusk Singers, for whom he also wrote the Svensktoppen hits "Älska Mig" and "Drömmarnas Golv". He decided to produce an album with Josefin Nilsson from this quartet, resulting in the 1993 English-language album Shapes, featuring ten new Andersson/Ulvaeus compositions. In 1992, he wrote the introduction melody for the European football championship, which was organized by Sweden that year. From the late 1980s, he had worked on an idea for an epic Swedish language musical based on his affection for traditional folk music. The musical was to be based on The Emigrants novels by Swedish writer Vilhelm Moberg. Benny wrote all the music and Bjorn wrote the text using the original Swedish books as a guide. "Kristina från Duvemåla" was first released as a 3 CD set and scored # 1 singles “Du Musta finnas” and Guldet blev till sand”. In October 1995, the stage production premiered in Sweden. The musical ran successfully for almost five years, before closing in June 1999. Although he didn’t know it to start with Benny's next project was Mamma Mia!, Originally Benny said to Bjorn that he was okay with the idea and kept a low profile on the production. The musical has become a worldwide box-office blockbuster In 2000, Benny wrote the music for fellow Swede Roy Andersson's film Songs from the Second Floor (the music later re-recorded, featuring new lyrics, with BAO! with vocals by Helen Sjöholm). In 2002, Andersson was given an honorary professorship by the Swedish Government for his "ability to create high-class music reaching people around the world".

For the 2004 semi-final of the Eurovision Song Contest, staged in Istanbul thirty years after ABBA had won the contest in Brighton, Benny appeared briefly in a special comedy video made for the interval act, entitled "Our Last Video". Each of the four members of the group appeared briefly in cameo roles, it was billed as the first time the four had worked together since the group split. In fact, they each filmed their appearances separately. In April/May 2007, Benny worked on the film soundtrack for a film version of Mamma Mia!, re-recording the old ABBA songs with musicians from the old ABBA recording sessions. Mamma Mia the movie premiered on 18 July 2008 and has now become the most successful movie musical of all time and has been named the number one box office smash of 2008, and the biggest-selling DVD ever in the UK.  In 2007 he wrote the theme for Roy Andersson's next film, You, the Living, In 2007, he was elected a member of Royal Swedish Academy of Music, and in 2008 received an Honorary Doctorate from the Stockholm University Faculty of Humanities for contributing importantly both to the preservation and the growth of the Swedish folk music tradition. Benny currently performs with his own band called, BAO; "Benny Anderssons Orkester" ("Benny Andersson's orchestra"), utilising the vocal talents of fellow Swedes Helen Sjöholm (from Kristina from Duvemåla) and Tommy Körberg (of Chess fame), with lyrics to new material sometimes written by his song-writing partner and best-friend of 40 years, Björn Ulvaeus. BAO have released many albums to huge success in Sweden, all containing hit singles. BAO achieved a new record in Sweden on the Svensktoppen chart by staying there for 243 weeks with the song Du är min man ("You Are My Man"), sung by Helen Sjöholm. Benny composes primarily for his 'band' BAO! For a compilation album of the Glenmark duo Gemini, Benny had Björn write new Swedish lyrics for the re-recording of two old songs; Björn also wrote new English lyrics to older Swedish language songs for opera singer Anne Sofie Von Otter’s tribute album "I Let The Music Speak". Benny has written the music to songs recorded by Anders Ekborg ("Han Som Har Vunnit Allt"] and Barbara Dickson ("The Day The Wall Came Tumbling Down"). The song "Kärlekens Tid" -performed by Helen Sjöholm with BAO! - -has also been performed in English by opera baritone Bryn Terfel. In 2009 he performed with his band in London and released his first English language album featuring English versions of many BAO hits. The album also included a new Benny and Bjorn song, STORY OF A HEART. The CD under the name of “Benny Andersson Band” was a success reaching the UK Top 30 chart. The English language versions of Kristina från Duvemåla , now simply called Kristina premiered in New York in 2009.

Benny continues to tour with his band BAO! And he continues to write new music.