Kelly sang with orchestras led by Dick Stabile, Artie Shaw, and Al Donahue. In early 1941, she joined Glenn Miller’s orchestra, replacing Dorothy Claire and Marion Hutton.
Kelly originally performed solo, but also soon became the female lead of The Modernaires, originally a male trio, then a quartet, resulting in the group becoming a quintet of four male singers and herself. Her first recording with the group was “Perfidia”, on which they sang with Dorothy Claire.
In 1942, Glenn Miller went into World War II military service and his band broke up. The Modernaires continued with Kelly as lead singer until 1978, when she retired in favor of her daughter, who performed as Paula Kelly Jr. In the late 1970s, Kelly and The Modernaires kept Swing Era music alive with their performances in various venues.