She was born Vera Margaret Welch (Lynn was her grandmother's maiden name), in East Ham, London. She began singing at the age of seven. Her first radio broadcast, with the Joe Loss Orchestra, was made in 1935. She married clarinettist and saxophonist Harry Lewis in 1939. In 1940 she began her own radio series, Sincerely Yours.
Her "Auf Wiederseh'n Sweetheart" became the first record by a UK artist to top the US charts, and she appeared regularly on Tallulah Bankhead's US radio programme The Big Show.
She was appointed an OBE (Officer of the Order of the British Empire) in 1969 and a DBE (Dame Commander of the Order of the British Empire) in 1975.