In the early and mid-1960s, McCoo was a member of the Hi-Fi's, who often opened for Ray Charles. She had been invited to join the group by photographer Lamonte McLemore, who would himself join McCoo in the 5th Dimension. Other Hi-Fi members included Harry Elston and Floyd Butler, who later formed the Friends of Distinction. She met Billy Davis, Jr. in 1966 when he established the 5th Dimension, then called the Versatiles, which also included Ron Townson and Florence LaRue. The group's first big hit was with 1967's "Up, Up and Away", written by Jimmy Webb. The song won four 1968 Grammy Awards and was the title track to 5th Dimension's first hit LP. A year later, the group recorded Laura Nyro's "Stoned Soul Picnic". A medley of "Aquarius/Let the Sunshine In" (from the musical "Hair") reached No. 1 on the "Billboard" Hot 100 chart in April to May 1969 and won the Grammy for 'Record of the Year'. The group's recording of another Nyro composition, "Wedding Bell Blues", featuring McCoo's most prominent vocal of that period, topped the Hot 100 in November 1969.