The founding members of the group were Conleth (Con) Cluskey (born 18 November 1941), Declan (Dec) Cluskey (born 23 December 1942), and John Stokes (Sean James Stokes) (born 13 August 1940). They formed their first band together in 1957: "The Harmonichords" (also seen as "The Harmony Chords"), a classically styled instrumental harmonica-act.

As the Harmonichords, they appeared on Hughie Green's Opportunity Knocks on Radio Luxembourg and on the 'Ed Sullivan' TV show St. Patrick's Day special (filmed in Dublin, broadcast 15 March 1959), where they played "Danny Boy"They also played background music plus featured pieces in a 25-week radio comedy series called Odd Noises on Radio Éireann, which featured Eamonn Andrews. In 1960, they changed their name to the Bachelors at the suggestion of Dick Rowe, A&R at Decca Records, who reportedly recommended the name "because that's the kind of boy a girl likes"

During the 1960s they had many successful songs in music charts in Europe, Australia, South Africa, South America, parts of the USSR, and the United States. Some of the most successful were "Charmaine" (1963); "Diane", "I Believe" (1964), "Ramona" and "I Wouldn't Trade You for the World" (1964); "Marie" (written by Irving Berlin) and "In the Chapel in the Moonlight" (1965). In 1965 they had the 'most played juke box track' with "The Stars Will Remember", from a film they made with then-current DJ Sam CostaTheir last big hit in the UK was a cover of the Paul Simon song "The Sound of Silence" which reached No. 3 in April 1966.