Edith Piaf certainly wrote and recorded the original French song Hymne a l'Amour which has the same tune, but the English language version was first recorded by Vera Lynn. It has since been recorded by several other (nearly all female artists) but the only person to take it into the UK singles charts was Mary Hopkin in 1976.
Sorry, let me get this right. Piaf did record the English version, but Mary Hopkin remains the only person to have a UK hit with it. There were also some musical amendments to Piaf's melody.